Showing papers by "University of Bristol published in 1975"
TL;DR: In this paper, the authors present an explanation of these findings in terms of the operation of social comparison processes between groups based on the need for a positive ingroup identity, which can be analyzed as a form of social competition.
Abstract: Recent studies have reported that the variable of social categorization per se is sufficient for intergroup discrimination. This paper presents an explanation of these findings in terms of the operation of social comparison processes between groups based on the need for a positive ingroup identity. The relationship between perceived social identity and intergroup comparison is elaborated theoretically, and it is argued that social comparisons give rise to processes of mutual differentiation between groups which can be analyzed as a form of ‘social’ competition. Social competition is distinguished from realistic competition (conflict of group interests). New data is reported which strengthens this interpretation of the ‘minimal’ categorization studies. It is found that minimal intergroup discrimination takes place in the distribution of meaningless ‘points’ as well as monetary rewards and that social categorization per se does not lead to intergroup behaviour where the subjects can act directly in terms of ‘self’. Other studies on intergroup biases are reviewed to argue for the generality of social competition in intergroup situations.
1,271 citations
TL;DR: Among predictors of an unfavourable outcome were found a relatively late age of onset, a longer duration of illness, previous admissions to psychiatric hospitals, a disturbed relationship between the patient and other members of the family, and premorbid personality difficulties.
Abstract: This is a prognostic study on 41 patients with anorexia nervosa (including three males) who satisfied defined diagnostic criteria. The patients had all been admitted to a metabolic unit where the mainstay of treatment was nursing care aimed at rapid restoration of body weight. A follow-up was conducted after a minimum lapse of four years after each patient's discharge from hospital. The outcome of the patient's illness was expressed in terms of an 'average outcome score' and a 'general outcome'. The series included a relatively high proportion of patients with a long illness who had received previous psychiatric treatment. Their families tended to come from higher social classes; a disturbed relationship with the patient was frequent. Premorbid disturbances in personality development were also common. The immediate response to treatment was excellent, with the majority of the patients returning to a normal weight, but relapses after discharge were common and readmissions were necessary in half the patients. At follow-up, the patients fell into the following defined categories: 'good' (39%), 'intermediate' (27%), 'poor' (29%), died (5%). Most of the patients who failed to recover continued to display the clinical features characteristic of anorexia nervosa. Among predictors of an unfavourable outcome were found a relatively late age of onset, a longer duration of illness, previous admissions to psychiatric hospitals, a disturbed relationship between the patient and other members of the family, and premorbid personality difficulties. It is suggested according to the severity of their illness, rather than on the method of treatment itself. The illness may last several years before eventual improvement or recovery, and a follow-up study must be extended over at least four years to be meaningful. An accurate prediction of eventual outcome is almost impossible, but late recoveries justify an optimistic outlook and continued therapeutic endeavour.
721 citations
TL;DR: In this paper, a line of uniaxial extension or a plane of pure shear passing through an orifice is used to extrude a continuous filament having a highly crystalline core in a generally less crystalline matrix.
Abstract: Molten crystallizable polymer is extruded through an orifice. Opposite the orifice on the upstream side is a fixed surface arranged so as to provide in the molten polymer a line of uniaxial extension or a plane of pure shear passing through the orifice. The polymer is extruded at a temperature and flow rate such as to cause a core of crystalline polymer to form in the melt along said line or plane. It is particularly suitable for extruding a continuous filament having a highly crystalline core in a generally less crystalline matrix of the polymer.
493 citations
TL;DR: The possibility that pyruvate transport into mitochondria may be rate limiting and involved in the regulation of gluconegenesis is discussed, and alpha-cyano-4-hydroxycinnamate was shown to be accompanied by the transport of a proton (or by exchange with an OH-ion), which allowed measurements of pyruVate transport at higher temperatures to be made.
Abstract: 1. Studies on the kinetics of pyruvate transport into mitochondria by an 'inhibitor-stop' technique were hampered by the decarboxylation of pyruvate by mitochondria even in the presence of rotenone. Decarboxylation was minimal at 6 degrees C. At this temperature the Km for pyruvate was 0.15 mM and Vmax. was 0.54nmol/min per mg of protein; alpha-cyano-4-hydroxycinnamate was found to be a non-competitive inhibitor, Ki 6.3 muM, and phenyl-pyruvate a competitive inhibitor, Ki 1.8 mM. 2. At 100 muM concentration, alpha-cyano-4-hydroxycinnamate rapidly and almost totally inhibited O2 uptake by rat heart mitochondria oxidizing pyruvate. Inhibition could be detected at concentrations of inhibitor as low as 1 muM although inhibition took time to develop at this concentration. Inhibition could be reversed by diluting out the inhibitor. 3. Various analogues of alpha-cyano-4-hydroxycinnamate were tested on rat liver and heart mitochondria. The important structural features appeared to be the alpha-cyanopropenoate group and the hydrophobic aromatic side chain. Alpha-Cyanocinnamate, alpha-cyano-5-phenyl-2,4-pentadienoate and compound UK 5099 [alpha-cyano-beta-(2-phenylindol-3-yl)acrylate] were all more powerful inhibitors than alpha-cyano-4-hydroxycinnamate showing 50% inhibition of pyruvate-dependent O2 consumption by rat heart mitochondria at concentrations of 200, 200 and 50 nM respectively. 4. The specificity of the carrier for its substrate was studied by both influx and efflux experiments. Oxamate, 2-oxobutyrate, phenylpyruvate, 2-oxo-4-methyl-pentanoate, chloroacetate, dichloroacetate, difluoroacetate, 2-chloropropionate, 3-chloropropionate and 2,2-dichloropropionate all exchanged with pyruvate, whereas acetate, lactate and trichloroacetate did not. 5. Pyruvate entry into the mitochondria was shown to be accompanied by the transport of a proton (or by exchange with an OH-ion). This proton flux was inhibited by alpha-cyano-4-hydroxycinnamate and allowed measurements of pyruvate transport at higher temperatures to be made. The activation energy of mitochondrial pyruvate transport was found to be 113 kJ (27 kcal)/mol and by extrapolation the rate of transport of pyruvate at 37 degrees C to be 42 nmol/min per mg of protein. The possibility that pyruvate transport into mitochondria may be rate limiting and involved in the regulation of gluconegenesis is discussed. 6. The transport of various monocarboxylic acids into mitochondria was studied by monitoring proton influx. The transport of dichloroacetate, difluoroacetate and oxamate appeared to be largely dependent on the pyruvate carrier and could be inhibited by pyruvate-transport inhibitors. However, many other halogenated and 2-oxo acids which could exchange with pyruvate on the carrier entered freely even in the presence of inhibitor.
483 citations
TL;DR: The quantitative analysis by gas chromatography of monosaccharides present in glycoproteins and glycopeptides using methanolysis, followed by re-N-acetylation and trimethylsilylation gives rise to several peaks for each monosACcharide, which provide for the unambiguous interpretation of the gas chromatograms obtained in the application of this g.l.c.c-mass spectrometry method.
Abstract: The quantitative analysis by gas chromatography of monosaccharides present in glycoproteins and glycopeptides using methanolysis, followed by re-N-acetylation and trimethylsilylation, gives rise to several peaks for each monosaccharide. The identity of these peaks for xylose, fucose, mannose, galactose, glucose, N-acetylglucosamine, N-acetylgalactosamine and N-acetylneuraminic acid was established for alpha- and beta-methyl pyranosides and furanosides by combined g.l.c.-mass spectrometry and proton-magnetic-resonance spectroscopy. These data provide for the unambiguous interpretation of the gas chromatograms obtained in the application of this g.l.c. method, and supply basic information for the further application of mass spectrometry in this field.
327 citations
TL;DR: It is argued that for ballistic movements the hands are equipotential, and skill is a direct function of practice, and ambilaterals, especially those with very mixed preferences, have virtually two non-preferred hands in continuously controlled movement tasks, and may therefore reply on ballistic movements more than do pronounced sinistrals and dextrals.
Abstract: Subjects classified according to degree of hand perference were tested with both hands on two tasks of controlled movement. Strongly lateralized subjects (both left- and right-handers) showed greater skill with their better hand than ambilaterals on a visually controlled aiming test (faster speed and equal errors), but there was no marked differences between groups with the other hand. Between-hand differences were also greater in lateralized subjects. On a ballistic rhythmical tapping test, no marked differences in speed were found, but ambilaterals made slightly fewer errors with the better hand. It is argued (i) that for ballistic movements the hands are equipotential, and skill is a direct function of practice, (ii) that the essential dexterity difference between the preferred and non-preferred hands is in the sensory or feedback control of movements rather than in motor function per se, and (iii) ambilaterals, especially those with very mixed preferences, have virtually two non-preferred hands in continuously controlled movement tasks, and may therefore reply on ballistic movements more than do pronounced sinistrals and dextrals.
280 citations
TL;DR: In this paper, the stability of parallel shear flow of an inviscid compressible fluid is investigated by a linear analysis and a subsonic neutral solution of the stability equation may be found when the basic flow is represented by the hyperbolic-tangent velocity profile.
Abstract: The stability of parallel shear flow of an inviscid compressible fluid is investigated by a linear analysis. The extension of the Rayleigh stability criterion and Howard's semi-circle theorem to compressible flows, obtained by Lees & Lin (1946) and Eckart (1963) respectively, are each rederived by a different approach. It is then shown that a subsonic neutral solution of the stability equation may be found when the basic flow is represented by the hyperbolic-tangent velocity profile. With the aid of this solution, the unstable eigenvalues, eigenfunctions and Reynolds stress are determined by numerical methods. A brief discussion of the results follows.
269 citations
01 Nov 1975
TL;DR: In this article, an invertor-output frequency range analysis is presented, using a 3-dimensional modulation-model approach, and the results of this analysis provide the system designer with generalised frequency-spectra characteristics for any particular frequency ratio and modulation depth.
Abstract: Sinusoidal p.w.m. invertors depend intrinsically for their operation on quite complex modulation processes. An in-depth study of these modulation processes is presented and the sources of possible operational problems are identified. These problems are shown to be manifest in low-frequency harmonic distortion and the possible existence of subharmonics at noninteger frequency ratios, particularly at low-frequency ratios. These problems restrict the viable invertor-output frequency range. A new method of control is presented which overcomes these problems and allows the possibility of low-frequency-ratio operation, resulting in significantly wider invertor-output frequency ranges. An analytic comparison of both the existing and new methods of control is presented, using a 3-dimensional modulation-model approach. The results of this analysis provide the system designer with generalised frequency-spectra characteristics for any particular frequency ratio and modulation depth by direct inspection.
262 citations
TL;DR: It is presented that in both adipose tissue and heart muscle, differences in activity of pyruvate dehydrogenase in the intact tissue persist during preparation and subsequent incubation of mitochondria.
Abstract: Dichloroacetate and other halogenated carboxylic acids can activate pyruvate dehydrogenase in rat heart and in rat heart mitochondria by effecting conversion of phosphorylated (inactive) pyruvate dehydrogenase into an active (dephosphorylated) form. These compounds are inhibitors of pig heart pyruvate dehydrogenase kinase. Pig heart pyruvate dehydrogenase phosphate phosphatase requires both Mg2+and Ca2+ for activity. Evidence is given for a dual metal requirement of the phosphatase in rat fat cell mitochondria. It is concluded that Mg2+ and Ca2+ are essential cofactors for the phosphatase but that their physiological significance as regulators remains to be established. Pig heart pyruvate dehydrogenase kinase is inhibited by high concentrations of magnesium and by low concentrations of calcium.
249 citations
01 May 1975
TL;DR: A powerful method of analysing and synthesising these complex modulation processes using a 3-dimensional modulation-model approach is presented, which provides a lucid geometric interpretation of the processes involved.
Abstract: It is axiomatic that frequency changing, whether it be in communications or power convertors, can only be achieved by a process of modulation. The paper presents a powerful method of analysing and synthesising these complex modulation processes using a 3-dimensional modulation-model approach, which provides a lucid geometric interpretation of the processes involved. The application of the new approach is demonstrated by deriving new frequency-spectra results for the p.w.m. and p.a.m. convertors, thereby providing essential design information.
226 citations
TL;DR: Fibrous atherosclerotic plaques contain proportions of these two collagens which are different from those occurring in normal arterial wall, which is largely responsible for the occlusive and irreversible nature of coronary and cerebral arterial disease.
Abstract: COLLAGEN comprises 40–60% of the protein1,2 and 30% of the weight3 of human fibrous atherosclerotic plaques. Its deposition in the arterial intima is largely responsible for the occlusive and irreversible nature of coronary and cerebral arterial disease. Four genetically distinct types of collagen have been identified in mammalian tissues and atleast five structural genes are involved in their synthesis4. The transcription of these various genes seems to be tissue specific. Type I collagen is found in tendon, bone and adult skin, type II is found in cartilage and intervertebral disk, and type IV is restricted to basement membrane. Type III collagen was observed first in newborn human skin5 and has been isolated and characterised from human aorta and leiomyoma6. Initial reports identified both types I and III in human aorta4,7. We have now found that fibrous atherosclerotic plaques contain proportions of these two collagens which are different from those occurring in normal arterial wall.
TL;DR: Combination of ion selective probes with microelectrodes which measure substrate and oxygen availability extend the information which can be obtained about ionic composition of cellular environment and the factors which are important in its homostasis.
Abstract: The development of ion selective microelectrodes has made it possible to measure the normal steady state in the pericellular environment together with ion fluxes in response to physiological or pathological disturbances. Combined intracellular and extracellular measurements indicate that there is a considerable range of ability between various types of cells in the efficiency with which they can tolerate changes in pericellular conditions. Macrophages are extremely tolerant while cells of the cerebral cortex require a very finely controlled local environment. Combination of ion selective probes with microelectrodes which measure substrate and oxygen availability extend the information which can be obtained about ionic composition of cellular environment and the factors which are important in its homostasis.
TL;DR: Studies with whole-cell preparations incubated in vitro indicate that alpha-cyano-4-hydroxycinnamate oralpha-cyanocinnamate can be used to specifically inhibit mitochondrial pyruvate transport within cells and thus alter the metabolic emphasis of the preparation.
Abstract: 1. Effects of alpha-cyano-4-hydroxycinnamate and alpha-cyanocinnamate on a number of enzymes involved in pyruvate metabolism have been investigated. Little or no inhibition was observed of any enzyme at concentrations that inhibit completely mitochondrial pyruvate transport. At much higher concentrations (1 mM) some inhibition of pyruvate carboxylase was apparent. 2. Alpha-Cyano-4-hydroxycinnamate (1-100 muM) specifically inhibited pyruvate oxidation by mitochondria isolated from rat heart, brain, kidney and from blowfly flight muscle; oxidation of other substrates in the presence or absence of ADP was not affected. Similar concentrations of the compound also inhibited the carboxylation of pyruvate by rat liver mitochondria and the activation by pyruvate of pyruvate dehydrogenase in fat-cell mitochondria. These findings imply that pyruvate dehydrogenase, pyruvate dehydrogenase kinase and pyruvate carboxylase are exposed to mitochondrial matrix concentrations of pyruvate rather than to cytoplasmic concentrations. 3. Studies with whole-cell preparations incubated in vitro indicate that alpha-cyano-4-hydroxycinnamate or alpha-cyanocinnamate (at concentrations below 200 muM) can be used to specifically inhibit mitochondrial pyruvate transport within cells and thus alter the metabolic emphasis of the preparation. In epididymal fat-pads, fatty acid synthesis from glucose and fructose, but not from acetate, was markedly inhibited. No changes in tissue ATP concentrations were observed. The effects on fatty acid synthesis were reversible. In kidney-cortex slices, gluconeogenesis from pyruvate and lactate but not from succinate was inhibited. In the rat heart perfused with medium containing glucose and insulin, addition of alpha-cyanocinnamate (200 muM) greatly increased the output and tissue concentrations of lactate plus pyruvate but decreased the lactate/pyruvate ratio. 4. The inhibition by cyanocinnamate derivatives of pyruvate transport across the cell membrane of human erythrocytes requires much higher concentrations of the derivatives than the inhibition of transport across the mitochondrial membrane. Alpha-Cyano-4-hydroxycinnamate appears to enter erythrocytes on the cell-membrane pyruvate carrier. Entry is not observed in the presence of albumin, which may explain the small effects when these compounds are injected into whole animals.
TL;DR: In this paper, X-ray diffraction measurements have been made on five nematogens in the nematic and isotropic liquid phases and the data have been interpreted to give information about the molecular packing.
Abstract: X-ray diffraction measurements have been made on five nematogens in the nematic and isotropic liquid phases. The data have been interpreted to give information about the molecular packing. Two Schiff's bases R1 [MATH] CH = N [MATH] R2 : MBBA (R1 = CH3O, R2 = nC4H9) and EBBA (R1 = C2H5O, R2 = nC4H9) have very similar structures, the higher homologue being much the more ordered. A third Schiff's base MBCA (R1 = CH3O, R2 = CN) is thought to have a more crystal-like packing resulting in a repeat distance ("d" spacing) along the texture axis 3 A shorter than the molecular length. Two cyanobiphenyls R [MATH] CN : 5 CB (R = C5H11) and 7 CB (R = C7H15) have very similar structures, with pronounced local ordering. This is revealed most strikingly in a repeat distance along the texture axis of ~ 1.4 molecular lengths, which is interpreted as arising from an overlapping head to tail arrangement of molecules resulting in a quasi-layer (smectic A) structure on a local scale. The order extends over 100-150 molecules and is more pronounced for the higher homologue. In all cases, local order very similar to that in the nematic phase persists in the isotropic liquids.
TL;DR: The cytochromes produced during aerobic growth were immunologically indistinguishable from those produced during photosynthesis, and the implications of these results to energy coupling in the photosynthetic bacteria are discussed.
TL;DR: Tajfel as discussed by the authors described a brief encounter with Albert Hirschman, who asked what was I going to talk about at the University of Michigan, and he briefly answered in (I hope) no more than five minutes.
Abstract: As I Ishared until recently the puzzlement of M. Jourdain in not knowing that I was writing prose, it would perhaps be appropriate to introduce these notes with an account of a brief encounter. Early in March 1974, I was spending a few days in Cambridge, Mass., on my way to deliver some lectures at the University of Michigan. When visiting some friends, I met for the first time Albert Hirschman who a little later in the evening asked me the kind of question that no well-drilled academic ever should in such circumtances take seriously or, even less, answer seriously : what was I going to talk about at Ann Arbor? But the question was asked with great courtesy and apparent interest; therefore I briefly answered in (I hope) no more than five minutes. Next morning, Hirschman appeared bearing a &dquo;slim volume&dquo; with the inscription: &dquo;Pour Henri Tajfel, avec le pressentiment d’un dialogue&dquo;. The book was his Exit, voice and loyalty 1. The present notes are a first step towards validating the self-fulfilling prophecy of that inscription. Amongst the major themes of the Ann Arbor lectures (Tajfel, 1974a) 2
Abstract: SUMMARY
A wick feed method was used to recrystallize a range of different plant epicuticular waxes from solutions in organic solvents. Using the scanning electron microscope the ultrastructure of the recrystallized wax from each species was compared with that of the wax on the corresponding intact plant surface and in many cases was found to be similar. It is concluded that the crystal structure of epicuticular waxes is greatly influenced by their inherent chemical and physical properties rather than by properties of the underlying cuticular membrane or by any mechanism of extrusion or transport of the wax to the plant surface.
TL;DR: Simple aliphatic monoamines are formed in the red algae by a non-specific amino acid carboxy-lyase with broad substrate specificity, and several new polyamine alkaloids have been characterized.
TL;DR: Water stimulation of receptors in the larynx of the lamb can produce apnea lasting as long as the water remains, although the discharge characteristics of these receptors are dissimilar to taste units they are unlikely to be taste buds.
TL;DR: Results are presented which show that when perfused rat heart is stimulated by 1 O6 M adrenaline there is a time dependent increase in phosphorylation of troponin-I which coincides with the increase in force of contraction.
TL;DR: The inhibition of pyruvate oxidation by diabetes and by oxidation of fatty acids and ketone bodies is considered to be of crucial importance in the selection of fuels for respiration and in the metabolic changes in heart and other tissues in diabetes and starvation.
Abstract: OXIDATION of pyruvate in perfused rat heart is inhibited by diabetes and by oxidation of fatty acids and ketone bodies1. Enhanced release and oxidation of fatty acids from muscle glycerides may be an important factor in the effects of diabetes2–4. These effects on pyruvate oxidation have generally been attributed to inhibition of pyruvate dehydrogenase, and regulation of this enzyme is considered to be of crucial importance in the selection of fuels for respiration and in the metabolic changes in heart and other tissues in diabetes and starvation.
TL;DR: It was concluded that feather pecking and cannibalism are separate phenomena, although the same cage conditions increased the incidence of both.
Abstract: 1. The progress of feather pecking and cannibalism was recorded from hatching to end of lay in a flock of caged layers and the influence of group size, floor area allowance and cage tier upon the incidence of these activities during lay assessed. 2. The largest group suffered more cannibalism and feather pecking than smaller groups, floor area allowance and tier being less important factors. 3. A significant trend was found for one death from cannibalism to be followed by more in the same cage.4. It was concluded that feather pecking and cannibalism are separate phenomena, although the same cage conditions increased the incidence of both. 5. Cannibalism may be divided into vent pecking and cannibalism affecting other parts of the body, the former is independent of feather pecking and the latter, though usually preceded by feather pecking, is only indirectly associated with it.
TL;DR: There appears to be a rapid turnover of protoheme in the absence of net synthesis and both pigments probably originate from a single 5-aminolevulinic acid pool, which is discussed in the light of current knowledge about tetrapyrrole regulation in photosynthetic organisms.
Abstract: Studies in which (14)C-labeled precursors were fed to etiolated barley leaves (Hordeum vulgare L. var. Proctor) yielded chlorophyll and protoheme having similar specific radioactivities. These findings indicate: (a) there appears to be a rapid turnover of protoheme in the absence of net synthesis; (b) both pigments probably originate from a single 5-aminolevulinic acid pool; (c) the efficient utilization of glutamate-1-(14)C and the relatively poor utilization of glycine-2-(14)C suggest that 5-aminolevulinic acid is probably synthesized by a pathway other than 5-aminolevulinic acid synthetase (succinyl CoA-glycine succinyltransferase) in agreement with previously published work; (d) protoheme turnover appears to be faster under conditions which allow for rapid chlorophyll accumulation; (e) difference spectra indicate that mitochondrial cytochromes make a relatively minor contribution to the total heme in barley leaves. These findings are discussed in the light of current knowledge about tetrapyrrole regulation in photosynthetic organisms.
TL;DR: Small diameter fibres occurring in the bulk of the myotome are shown to differ from the superficial fibres with respect to their oxidative metabolism and myofibrillar A TPase, and the relevance of this finding to studies on the energetics and swimmin!t efficiency of this species are discussed.
Abstract: A histochemical study has been made on the myotomal musculature of the rainbow trout Salmo gairdneri Richardson. Four main types of fibre can be distinguished on the basis of differences in fibre size, lipid content and succinic dehydrogenase and myofibrillar adenosine triphosphatase activity (A TPase activity). Early histological studies have concluded that in addition to a superficial strip of muscle small diameter. red' fibres occur throughout the trout myotome. These small diameter fibres occurring in the bulk of the myotome are shown to differ from the superficial fibres with respect to their oxidative metabolism and myofibrillar A TPase. The relevance of this finding to studies on the energetics and swimmin!t efficiency of this species are discussed. I. INTRODUCnON . The myotome of most teleost fish is composed of distinct red and white muscles. The red muscle forms a thin sheet lying just underneath the lateral line, and runs from behind the head to the caudal fin. Red fibres are known to have high concentrations of myoglobin, cytochromes and lipids (George, 1962; Matsuura &
TL;DR: In this article, the authors examined the effect that appreciable molecular extension has on the crystallization of long chain molecules and showed that to achieve high molecular extensions in solution a longitudinal velocity gradient of strain rate about 103s-1 is required.
Abstract: This work examines the effect that appreciable molecular extension has on the crystallization of long chain molecules. Elementary theoretical considerations presented indicate that to achieve high molecular extensions in solution a longitudinal velocity gradient of strain rate about 103s-1 is required. A method of generating such a velocity gradient, involving flow between opposed jets, is reported and the nature of this flow pattern is examined and quantitatively analysed. The behaviour of polyethylene-xylene solutions in the flow field is presented, notably birefringence observations and measurements indicate that a high degree of molecular alinement can be achieved in specific localized areas of the flow field; also concentration effects are observed which are discussed in terms of entanglement concepts. The effect chain alinement has on crystallization is examined in detail, in particular the ‘shish kebab ’ morphology of the crystals so produced is examined in relation to the hydrodynamic conditions in which they were grown.
TL;DR: The properties of white muscle myofibrils from goldfish acclimated to 1°C and 26°C has been studied and the apparent energy of activation was found to be positively correlated with the adaptation temperature of the species.
TL;DR: In this article, the effect of ionizing radiation on polyethylene in the form of solution-grown single crystals was investigated, and it was shown that the radiation-induced effects along the fold surfaces could be significantly different from those within the crystal interior.
Abstract: An extensive study has been carried out on the effect of ionizing radiation on polyethylene in the form of solution-grown single crystals to follow up preceding investigations which had indicated that the radiation-induced effects along the fold surfaces could be significantly different from those within the crystal interior. In this first part of the series, radiation-induced crosslinking was investigated in the case of ''crystal core'' material. This material, obtained by removal of the fold surface by oxidative degradation with ozone, consists of isolated foldfree crystal layers of dicarboxylic acids of uniform length, the length itself depending on the fold length of the starting crystal. This ''core material'' was irradiated by $gamma$ rays and the effect of crosslinking was followed by GPC analysis by recording the development of dimer, trimer, etc., peaks in the chromatograms. For a given dose, the fractional amount of crosslinked material is independent of the chain length. This, together with other effects described, provides unambiguous evidence that crosslinking occurs at the chain ends or, in other words, that there is no crosslinking within the interior of the paraffinoid lattice. Further, no permanent scission was observed to occur within the lattice, at least in amounts detectable by themore » present molecular weight measurements. The obvious significance of these effects for radiation studies on paraffinoid substances in general, beyond those of the present long-chain dicarboxylic acids, is discussed prior to utilizing them in the study of chain-folded polyethylene crystals in the following parts of the series. (auth)« less
TL;DR: The suggestion is made that the oxidative pentose phosphate pathway can provide the NADPH required for chlorophyll biosynthesis during the early stages of greening.
Abstract: 1. Chlorophyll (ide) formation from protochlorophyll (ide) that is normally inactive was demonstrated in etioplast membranes isolated from maize and barlley plants, the process being dependent on intermittent illumination and the addition of NADPH. 2. The addition of NADPH to the membranes was shown to result in the conversion of inactive protochlorophyll (ide) absorbing at about 630 nm into a form(s) with light-absorption maxima at about 640 and 652 nm, both of which disappear when chlorophyll (ide) is formed on illumination. 3. The temperature-dependence of the activation process and its response to a variety of reagents were examined. From these, the conclusion is drawn that -SH groups are involved in the activation but in the active complex these are unavailable for reaction with -SH reagents. 4. Evidence is presented for the occurrence of glucose 6-phosphate dehydrogenase activity within etioplasts and the suggestion is made that the oxidative pentose phosphate pathway can provide the NADPH required for chlorophyll biosynthesis during the early stages of greening.