Showing papers by "University of Dundee published in 1979"
TL;DR: In this paper, the characteristics of an insulated-gate field effect transistor made from amorphous silicon (a-Si) deposited in a glow discharge are discussed, and it is suggested that the a-Si device could be applied with advantage in an addressable matrix of a liquid-crystal display panel.
Abstract: The characteristics of an insulated-gate field-effect transistor made from amorphous silicon (a-Si) deposited in a glow discharge are discussed. It is suggested that the a-Si device could be applied with advantage in an addressable matrix of a liquid-crystal display panel.
362 citations
338 citations
TL;DR: Results demonstrated that the activation by Calmodulin was caused by the interaction of a second molecule of calmodulin with phosphorylase kinase, and the existence of an additional calmodul binding site was also indicated by the finding that phosphory lase kinases bound to cal modulin-Sepharose in the presence of calcium ions.
Abstract: Phosphorylase kinase from rabbit skeletal muscle has been shown to possess the structure (αβγδ)4, where the δ-subunit is identical to the calcium binding protein, termed calmodulin. The amount of calmodulin was found to be stoichiometric with the α, β and γ subunits in all preparations of phosphorylase kinase, and was not dissociated from the enzyme even in the presence of 8 M urea, provided that calcium ions were present.
The activity of phosphorylase kinase was increased by the addition of calmodulin to the assay, and half-maximal activation was observed at a molar ratio, calmodulin/phosphorylase kinase, of 20:1. At saturating concentrations of calmodulin, all preparations of phosphorylase kinase had a specific activity of 13.5 ± 1.0 U/mg at pH 8.2. In the absence of calmodulin, the specific activity ranged from 2–7 U/mg, so that the stimulation by calmodulin varied from 2–7-fold with different preparations of phosphorylase kinase. The molecular basis for this variability is discussed.
The stimulation of the activity by calmodulin was prevented by the addition of troponin-I or the antipsychotic drug trifluoperazine, whereas these compounds had little effect on the calcium-dependent activity in the absence of calmodulin. These results demonstrated that the activation by calmodulin was caused by the interaction of a second molecule of calmodulin with phosphorylase kinase. The existence of an additional calmodulin binding site was also indicated by the finding that phosphorylase kinase bound to calmodulin-Sepharose in the presence of calcium ions.
Experiments with ICR/IAn mice which lack muscle phosphorylase kinase activity and C3H/He-mg mice with normal activity, demonstrated that when muscle extracts were fractionated with ammonium sulphate, 90–95% of the calmodulin which precipitated at 0–35% ammonium sulphate was bound to phosphorylase kinase. This information was used to show that at least 35% of the calmodulin in low ionic strength EDTA extracts of rabbit skeletal muscle was bound to phosphorylase kinase.
Muscle extracts from ICR/IAn mice and C3H/He-mg mice had identical myosin light-chain kinase activities, showing that there was not a generalized defect in calmodulin-dependent enzymes in ICR/IAn mice. The skeletal muscle extracts of ICR/IAn mice contained 60% of the calmodulin found in C3H/He-mg mice, and addition of calmodulin did not restore phosphorylase kinase activity to muscle extracts prepared from ICR/IAn mice. This indicated that the lack of phosphorylase kinase activity was not caused by an absence of the calmodulin molecule.
The role of calmodulin in the regulation of muscle phosphorylase kinase activity is discussed.
251 citations
TL;DR: Attachment of virus particles to antiserum-coated electron microscope grids (immunosorbent electron microscopy) provided a test that was at least a thousand times more sensitive for detecting potato leafroll (PLRV) and potato mop-top (PMTV) viruses.
Abstract: SUMMARY
Attachment of virus particles to antiserum-coated electron microscope grids (immunosorbent electron microscopy) provided a test that was at least a thousand times more sensitive than conventional electron microscopy for detecting potato leafroll (PLRV) and potato mop-top (PMTV) viruses. The identity of the attached virus particles was confirmed by exposing them to additional virus antibody, which coated the particles.
PLRV particles (up to 50/μm2 of grid area) were detected in extracts of infected potato leaves and tubers, infected Physalis floridana leaves, and single virus-carrying aphids. On average, Myzus persicae yielded 10–30 times more PLRV particles than did Macrosiphum euphorbiae.
PMTV particles (up to 10/μm2 of grid area) were detected in extracts of inoculated tobacco leaves, and of infected Arran Pilot potato tubers with symptoms of primary infection. Particles from tobacco leaves were of two predominant lengths, about 125 nm or about 290 nm, and fewer particles of other lengths were found than in previous work, in which partially purified or purified preparations of virus particles were examined, using grids not coated with antiserum.
153 citations
TL;DR: The results imply that the phosphorylation of inhibitor-1 may be equally as important as the phosph Corylase kinase in elevating the levels of phosphorylase a in skeletal muscle in vivo.
Abstract: Inhibitor-1 has been shown to be phosphorylated in skeletal muscle in vivo. In normal fed animals the degree of phosphorylation was 31 ± 7% and this value increases to 70 ± 12% following an intravenous injection of adrenaline.
The results imply that the phosphorylation of inhibitor-1 may be equally as important as the phosphorylation of phosphorylase kinase in elevating the levels of phosphorylase a. The role of inhibitor-1 in metabolism is discussed.
136 citations
TL;DR: In this paper, the physiological responses of rainbow trout to sudden changes in salinity were investigated and an initial period lasting about 8 h was characterized by increased drinking and an increase in plasma and body ions.
Abstract: Physiological responses of rainbow trout (mean weight 13.3 g) to sudden changes in salinity were investigated. An initial period lasting about 8 h was characterized by increased drinking and an increase in plasma and body ions. Fish failed to survive more than 2 days in full strength sea water but in two-thirds sea water there were few mortalities and adaptation was complete in 7–10 days. During this period there were gradual physiological changes resulting in normal plasma ion concentrations but significantly increased body ionic content. The intracellular concentrations of muscle chloride showed the greatest increase.
128 citations
TL;DR: Experiments in dune sands gave better growth with both these endophytes than with either alone, but indicated the complexity of interaction between host, endophyte and edaphic factors, and the possible significance of mycorrhizas in nutrientpoor and unstable habitats is discussed.
Abstract: In a sand-dune system at Tentsmuir Point, Fifeshire, Scotland, Glomus fasciculatus was the only endophyte present on roots of pioneer colonizing grasses. This fungus formed sporocarps and spore aggregates in the soil and in association with organic fragments, particularly root tissues. Amounts of infection and external mycelium varied with vegetation zone and season, but both became greater with dune stabilization and infection increased during summer and autumn. Growth of Ammophila arenaria and Agropyron junceiforme in unsterile foreshore sand was improved when mycorrhizal with G. fasciculatus and G. macrocarpus var. geosporus . Experiments in dune sands, with maize as a test plant, gave better growth with both these endophytes than with either alone, but indicated the complexity of interaction between host, endophyte and edaphic factors. The possible significance of mycorrhizas in nutrientpoor and unstable habitats is discussed.
117 citations
01 Jan 1979
TL;DR: The cell populations constituting the caudate–putamen or neostriatum originate from the germinal epithelium of the developing neuraxis in the region of the Telodiencephalic junction and the adjacent parts of the telencephalon.
Abstract: Publisher Summary This chapter describes the ontogeny of the neostriatum. It presents the results of a series of studies on the development of the mouse neostriatum. The cell populations constituting the caudate–putamen or neostriatum originate from the germinal epithelium of the developing neuraxis in the region of the telodiencephalic junction and the adjacent parts of the telencephalon. The first evidence of major differentiation in this area is a swelling appearing in the mouse at embryonic day 11, which straddles the telodiencephalic boundary zone and, thus, protrudes into both the third and lateral ventricles. A day later, at E12, a second more gently sloping swelling develops in the adjacent part of the telencephalic wall. These are respectively the medial and lateral ventricular elevations. The ventricular elevations are the sites of production of the neurons and neuroglia of the basal parts of the telencephalon. The histological structure of each elevation is similar and reflects an enhanced proliferative capacity of the germinal epithelium. At E10, the presumptive sites of the elevations are composed of pseudostratified cells of the ependymal layer.
116 citations
TL;DR: Contact allergic sensitivity to oleoresin extract from Compositae plants was found to be usually present in individuals suffering from the photosensitivity dermatitis and actinic reticuloid syndrome.
Abstract: SUMMARY
Of sixty-nine examples of the photosensitivity dermatitis and actinic reticuloid syndrome, nine were found to be allergically sensitive to chrysanthemum oleoresin extract. Although this extract showed evidence in vitro of a phototoxic action we were unable with in vivo studies to explain the connection between the contact allergic sensitivity and the photosensitivity. The fractions responsible for the in vitro phototoxicity appear to be different from those involved in the in vivo contact allergic sensitivity. This study provides further support for the view that in the photosensitivity dermatitis and actinic reticuloid syndrome contact allergic sensitivity is of importance.
113 citations
TL;DR: Evidence is presented which demonstrates that glycogen synthase-2 is merely a modified form of phosphorylase kinase which has lost its ability to be regulated by calcium ions at pH 6.8, and the implications of these findings are considered.
Abstract: Homogeneous preparations of phosphorylase kinase from rabbit skeletal muscle catalyse a calcium-dependent phosphorylation of glycogen synthase a isolated from the same tissue. The calcium-dependent glycogen synthase kinase activity copurifies with phosphorylase kinase throughout the standard procedure for the isolation of the latter enzyme. At the final step of the purification, gel filtration on Sepharose 4B, the elution profiles for glycogen synthase kinase and phosphorylase kinase activities are identical. ICR/IAn mice, which lack muscle phosphorylase kinase activity, do not contain detectable calcium-dependent glycogen synthase kinase activity. These results indicate that the calcium-dependent phosphorylation of glycogen synthase is catalysed by phosphorylase kinase and not by another calcium-dependent protein kinase that might be contaminating the preparation.
The phosphorylation of glycogen synthase a by phosphorylase kinase reaches a plateau in the range 0.73 ± 0.1 molecules of phosphate incorporated per subunit and is accompanied by a 2-fold decrease in the activity in the absence of glucose 6-phosphate. The phosphorylation takes place on a unique serine residue located seven amino acids from the N-terminus of the polypeptide chain. The amino acid sequence surrounding serine-7 is similar to the amino acid sequence surrounding the phosphoserine in phosphorylase a.
Glycogen synthase kinase-2 is the name given to a protein kinase present as a trace contaminant in highly purified preparations of glycogen synthase [Nimmo, H. G. and Cohen, P. (1974) FEBS Lett. 47, 162–167]. Glycogen synthase kinase-2 also phosphorylates serine-7 exclusively, and evidence is presented which demonstrates that glycogen synthase kinase-2 is merely a modified form of phosphorylase kinase which has lost its ability to be regulated by calcium ions at pH 6.8.
The rate of phosphorylation of glycogen synthase a by phosphorylase kinase is 2–3-fold slower than the rate of phosphorylation of phosphorylase b when identical concentrations of the two protein substrates are used (6 μM). At physiological concentrations of glycogen synthase (0.3 mg/ml) and phosphorylase (8.0 mg/ml), the time required for half-maximal phosphorylation of each enzyme by phosphorylase kinase is similar. These results suggest that the phosphorylation of glycogen synthase by phosphorylase kinase may be physiologically significant, and the implications of these findings are considered.
104 citations
TL;DR: In this paper, the authors show that pseudotachylytes are preferentially formed in mica-rich domains due to release of water through disruption of the mica lattice by frictional sliding.
TL;DR: In this article, the authors describe and rationalise the deformation structures within a salt dome at Kuh-e-Namak (Dashti) and a substantial glacier of rock salt flows downslope north eastwards from the salt dome.
01 Jan 1979
TL;DR: The formation of appreciable amounts of non-specific FRP may interfere in the determination of the true enzyme activity and difficulties are illustrated with data obtained from an investigation of Meijer's semipermeable membrane technique for assaying acid phosphatase in unfixed sections of muscle.
Abstract: Some practical criteria are suggested for establishing the precision, reproducibility, validity and specificity of quantitative histochemical techniques used for assaying the activities of enzymes in single cells and tissue sections. To be valid, a technique should ideally pass 12 tests. Principally these involve proving that the mean absorbance or fluorescence of the specific final reaction product (FRP) is related to section thickness, incubation time, substrate concentration and the concentration of enzyme in situ. However, the formation of appreciable amounts of non-specific FRP may interfere in the determination of the true enzyme activity. This and other difficulties are illustrated with data obtained from an investigation of Meijer's semipermeable membrane technique for assaying acid phosphatase in unfixed sections of muscle.
TL;DR: Analysis of ionic regulation in adapted fish indicates that balance is maintained mainly by expending energy on Cl − regulation, which results in high tissue concentrations of these ions and eventual death in fish in full strength sea water.
Abstract: Small rainbow trout (5–20 g) adapt to salinities of up to at least 22‰ but not to full strength sea water. In adapted fish plasma ions are regulated nearthe fresh water values, but there is an ionic invasion of the tissues, particularly by Cl − in muscle cells. Analysis of ionic regulation in adapted fish indicates that balance is maintained mainly by expending energy on Cl − regulation. Fish in full strength sea water can no longer regulate Na + or Cl − in plasma or tissues, which results in high tissue concentrations of these ions and eventual death.
TL;DR: Calmodulin binds 4 Ca*‘/mol and the calcium binding properties of phosphorylase kinase support the view that all the high affinity binding sites for calcium are located on the 6-subunit, which suggests that the 6 -subunit is the compo- nent which confers calcium sensitivity to phosphoryLase.
TL;DR: On being shown the names of two towns geography students determined whether one of the towns was north of another by first accessing stored information that specifies a town's location only crudely; when this is insufficient to make the relevant inference more finely discriminating information is accessed.
Abstract: On being shown the names of two towns geography students determined whether one of the towns was north (say) of the other. Reaction time decreased as the distance between the towns increased. This finding was explained by supposing that subjects attempt to make inferences (about whether one town is north of another) by first accessing stored information that specifies a town's location only crudely; when this is insufficient to make the relevant inference more finely discriminating information is accessed. The explanation was supported in a second experiment: when one town was Scottish and the other English, reaction times were shorter than when both were English. This result was predicted from the assumption that the information first accessed specifies which country a town lies in: when one town is Scottish and the other English, this information can be used to make the correct inference without further specification of location (since all Scottish towns are north of all English towns), whereas when bot...
TL;DR: Variables such as social class, age and parity were not related to the level of emotional disturbance, but a history of marital problems, sexual difficulties, poor relationships with immediate family or disrupted family relationships in childhood were so related.
Abstract: Emotional disturbance was assessed in a group of women in the first few days following childbirth and again 2 months and 1 year following childbirth; the clinical features are described. Variables such as social class, age and parity were not related to the level of emotional disturbance, but a history of marital problems, sexual difficulties, poor relationships with immediate family or disrupted family relationships in childhood were so related. Twenty-four hour urinary excretion of cyclic AMP (adenosine 3'5' cyclic monophosphate) was estimated in the same group of women on 2 occasions in the week following childbirth and again 2-3 months later in approximately one third of the original sample. Excretion of cyclic AMP in the few days following delivery was elevated compared with excretion 2-3 months later, and there was a significant rise in urinary excretion of cyclic AMP between the 1st and 2nd urine collections. Those women showing most emotional disturbance on the 3rd day after delivery and women indicating most mood change in the direction of becoming elated had the highest levels of cyclic AMP in the 2nd urine collection.
TL;DR: Redox titrations performed in the presence of CO showed that one of the b-type cytochromes in the aerobically grown cultures was reduced, even at the upper limits of the range of electrode potentials (above +400mV).
Abstract: 1. Electron-transport particles derived from Escherichia coli grown aerobically contain three b-type cytochromes with mid-point oxidation–reduction potentials at pH7 of +260mV, +80mV and −50mV, with n=1 for each. The variation of these values with pH was determined. 2. E. coli develops a different set of b-type cytochromes when grown anaerobically on glycerol with fumarate or nitrate as terminal electron acceptor. Electron-transport particles of fumarate-grown cells contain b-type cytochromes with mid-point potentials at pH7 of +140mV and +250mV (n=1). These two cytochromes are also present in cells grown with nitrate as terminal acceptor, where an additional cytochrome b with a mid-point potential of +10mV (n=1) is developed. 3. The wavelengths of the α-absorption-band maxima of the b-type cytochromes at 77K were: (a) for aerobically grown cells, cytochrome b (Em7 +260mV), 556nm and 563nm, cytochrome b (Em7 +80mV), 556nm and cytochrome b (Em7−50mV), 558nm; (b) for anaerobically grown cells, cytochrome b (Em7 +250mV), 558nm, cytochrome b (Em7 +40mV), 555nm and cytochrome b (Em7 +10mV), 556nm. 4. Cytochrome d was found to have a mid-point potential at pH7 of +280mV (n=1). 5. Cytochrome a1 was resolved as two components of equal magnitude with mid-point potentials of +260mV and +160mV (n=1). 6. Redox titrations performed in the presence of CO showed that one of the b-type cytochromes in the aerobically grown cultures was reduced, even at the upper limits of our range of electrode potentials (above +400mV). Cytochrome d was also not oxidizable in the presence of CO. Neither of the cytochromes a1 was affected by the presence of CO.
TL;DR: Aldabra Atoll has been studied extensively in the last few decades as discussed by the authors, showing that there have been great variations in the land area of the atoll, the topography, and the height above sea level.
Abstract: Far from being fixed and unchanging, the islands and land areas of the western Indian Ocean are in a dynamic state; the most important variable, apart from tectonic activity, has been the rise and fall of sea level as a consequence of late Pleistocene glacial advances and retreats. Geological studies at Aldabra show that there have been great variations in the land area of the atoll, the topography, and the height above sea level. Moreover, the land has been completely submerged on at least two occasions. Fossil tortoises, crocodiles, lizards, birds and snails illustrate, if fragmentarily, the pattern of colonization and extinction on the Atoll. Although the earliest terrestrial deposits represent vegetated sandy cay habitats colonized by crocodiles, iguanas, petrels, tortoises and snails, the later deposits indicate dissected rocky substrates with meagre soil formation and scrub vegetation more similar to present day Aldabra. However, both the lizard and snail faunas indicate that considerable faunal change has occurred.
TL;DR: The acid/base balance showed no major changes but arterial fell greatly on transfer but by 5 h had returned to 82% of the normal level and after 24 h arterial had decreased markedly again and this continued to the end of the experiment.
Abstract: Ionic and respiratory parameters of large rainbow trout were measured during freshwater to seawater transfer. Branchial Cl− efflux increased immediately on transfer and urine excretion of Cl− increased after 14 h. Branchial Na+ efflux however did not start to build up until 4–5 h after transfer and there was no increase in urinary Na+ excretion. These differences are discussed.
TL;DR: A detailed study of the photoluminescence (PL) behavior of high TD, undoped, glow-discharge a-Si, prepared by the Dundee group, was made in this paper.
Abstract: A detailed study has been made of the photoluminescence (PL) behaviour of high TD, undoped, glow-discharge a-Si, prepared by the Dundee group. Our measurements include temperature and field quenching of the luminescence and PL decay in the region 2 ns to ∼20 μs. Some recombination models for a-Si are briefly reviewed in the light of these results. Preliminary life-time data on doped a-Si are also presented and used to discuss our earlier measurements on the PL efficiency of doped samples. We conclude that a distribution of radiative lifetimes is present in a-Si, due to disorder. The main competitive non-radiative process is tunnelling to defects.
TL;DR: The phospborylation of acetyl-Cola carboxylase by the purified catal:: iic subunit of cyclic AMPdependent protein kinase was found to take place at a very similar rate to that of other well established pbysiok@cal substrates of this enzyme, suggesting that the reaction was likely to occur in viva.
TL;DR: In this paper, the formation, profile and capacitance of the metal/a-Si barrier were investigated by means of model calculations based on the experimentally determined distribution of localized states.
Abstract: In a recent paper we investigated the formation, profile and capacitance of the metal/a-Si barrier by means of model calculations based on the experimentally determined distribution of localized states. This approach has been developed in the present paper and is used in a detailed comparison with capacitance measurements on Au/a-Si barriers. The a-Si specimens, either undoped or with donor concentrations of up to 2 × 1018 cm−3, were produced by the glow-discharge technique. It has been possible to give a satisfactory interpretation of the observed frequency, bias and temperature dependence of the barrier capacitance. For this two important aspects had to be included in the model calculations : first the electronic behaviour of the barrier, determined by the known space-charge distribution, and secondly the properties of the specimen in the measuring circuit, analysed by means of an equivalent circuit. In the final section of the paper we present current-voltage curves for different donor concent...
TL;DR: A quantitative lifespan study of changes in cell number, cell division and cell death in various regions of the mouse forebrain shows clear trends in both longevity and apoptosis.
Abstract: A quantitative lifespan study of changes in cell number, cell division and cell death in various regions of the mouse forebrain
A quantitative study of changes in total cell number was carried out in the indusium griseum and anterior commissure from fetal life to old age in the mouse brain. The changes in the number of mitotic and pyknotic cells were recorded in the indusium griseum, anterior commissure, subependymal and ependymal layers over the same period. The number of neurons which are produced and which migrate to the indusium griseum are in excess of the number eventually required and the surplus neurons are lost by cell death in late gestation and early postnatal life while synapto-genesis and neuronal differentiation is taking place. This neuronal loss is associated with a rapid turnover of glia. Most first generation glia, or their immediate precursors, are produced prenatally, in parallel but one day behind neurons. There is no large burst of mitotic activity in the postnatal brain which gives rise to the myelination gliosis which is probably largely a migratory phenomenon. Cell division continues throughout life in all parts of the brain studied. The greatest mitotic activity is centred in the subependymal layer where mitotic cells substantially outnumber pyknotic ones. There is a gradual decrease in mitotic activity in the subependymal layer up to 9 months of age with fairly constant mitotic activity thereafter. Mitotic activity in the indusium griseum levels out at 3 months post-natum with mitotic and pyknotic cells present in roughly equal numbers thereafter. Mitotic activity in all parts of the anterior commissure levels out at 6 months postnatum and remains constant thereafter. Mitotic and pyknotic cells are present in similar numbers except for a peak in pyknotic cells at 9 months. Cell number in the indusium griseum and anterior commissure is fairly constant between 3 and 9 months, but glial number begins to decrease in all parts of the anterior commissure from 12 to 22 months. In the indusium griseum the number of glia increased slightly between 6 and 22 months. The number of neurons fluctuated during the first week after birth then remained constant until 18 months. There was a significant decrease in the number of neurons between 18 and 22 months.
TL;DR: Differences were detected in the shoot height, shoot dry weight, standing crop biomass, leaf area index, crop growth rate and net efficiency of solar energy conversion among the three lochs.
Abstract: Studies were made on the development and production of Phragmites australis (Cav.) Trin. ex Steudel (= Phragmites communis Trin.) stands from Forfar Loch-polytrophic, Balgavies Locheutrophic and Loch of the Lowes-mesotrophic. Differences were detected in the shoot height, shoot dry weight, standing crop biomass, leaf area index, crop growth rate and net efficiency of solar energy conversion among the three lochs. Such differences were partly due to the different nutrient levels of the three locations. The percentage ratio of leaf to shoot weight, leaf area ratio, relative growth rate and net assimilation rate for the reed stands in the three lochs were also calculated and were compared with values from other study areas.
TL;DR: Segments of mouse pancreatic or exorbital lacrimal gland were superfused with saline solutions and acetylcholine was added locally to impaled acini by micro‐ionophoresis from an extracellular micropipette.
Abstract: 1. Segments of mouse pancreatic or exorbital lacrimal gland were superfused with saline solutions. Under visual control two micro-electrodes were inserted into neighbouring cells within the same acinus or into neighbouring acini. Cell to cell electrical coupling was assessed by injecting rectangular current pulses through one electrode and measuring the electrotonic potential change in the same cell (V1) and in the neighbouring cell (V2). Acetylcholine (ACh) was added locally to impaled acini by micro-ionophoresis from an extracellular micropipette.
2. Exposure of the tissues to a Krebs solution equilibrated with 100% CO2 caused a rapid increase in the size of electrotonic potential changes in the current injection cell and disappearance of the electrotonic potential changes in a neighbouring acinus or cell. This electrical uncoupling of previously coupled cells was rapidly reversible upon return to a solution equilibrated with 95% O2 and 5% CO2.
3. Reduction of electrical intercellular coupling was also obtained using smaller CO2 concentrations (50, 20 or 10%). In these cases the effects developed more slowly and were less dramatic. Reducing the extracellular HCO3 concentration enhanced the uncoupling effect of 10 or 20% CO2. However, weak uncoupling effects were still observed using 10 or 20% CO2 in combination with a high bicarbonate concentration maintaining a constant extracellular pH (7·4).
4. Reductions in extracellular pH (down to 5·5) achieved by varying combinations of Tris base and Tris HCl had no effect on electrical coupling. Brief periods of anoxia (100% N2) also had no effect.
5. Exposure to 20% CO2 markedly enhanced the uncoupling effect of a brief ionophoretic pulse of ACh.
6. Exposure of the tissue to 10 m M-NH4Cl, a procedure expected to increase the intracellular pH, counteracted the uncoupling effect of ACh. During sustained uncoupling caused by a sustained ACh stimulation a brief period of exposure to NH4Cl caused an immediate and fully reversible recoupling.
7. It is concluded that variations in intracellular pH have marked effects on the electrical coupling between neighbouring cells in the pancreatic and lacrimal acinar tissue.
TL;DR: A direct positive correlation between the size of the intracellular pool of glutamate and biosynthetic glutamine synthetase activity occurred during light/dark shifts, and on treatment with NH4+.
Abstract: Extractable glutamine synthetase activity of the cyanobacterium Anabaena cylindrica was reduced by approximately 50% when N2-fixing cultures were treated with 10 mM NH4+or were placed in darkness. The deactivated enzyme could be rapidly reactivated (within 5 min) by adding 40 mM 2-mercaptoethanol to the biosynthetic reaction mixture. The enzyme could also be reactivated in vivo by replacing the culture in light or by removing NH4+. When the enzyme was deactivated by simultaneously adding NH4+and placing the culture in darkness, reactivation occurred on reillumination and removal of NH4+. The removal of NH4+in darkness did not result in reactivation. On in vitro reactivation of glutamine synthetase from dark or NH4+-treated cultures the maximum glutamine synthetase activity observed frequently exceeded that of glutamine synthetase extracted from untreated cultures. Anacystis nidulans showed a similar type of reversible dark deactivation to A. cylindrica but Plectonema boryanum and a Nostoc did not. With A. cylindrica, a direct positive correlation between the size of the intracellular pool of glutamate and biosynthetic glutamine synthetase activity occurred during light/dark shifts, and on treatment with NH4+. The changes in activity of glutamine synthetase in A. cylindrica in response to light resemble in some respects the light modulation of enzymes of the oxidative and reductive pentose phosphate pathways noted in cyanobacteria by others.
TL;DR: The cyanobacterium Oscillatoria agardhii Gomont was cultivated with a diurnal light-dark cycle (photoperiod 16 h) in continuous culture and showed no evidence of phased synchrony, although this conclusion was contradicted by changes in DNA and pigments.
Abstract: The cyanobacterium Oscillatoria agardhii Gomont was cultivated with a diurnal light-dark cycle (photoperiod 16 h) in continuous culture. There were found to be large differences in specific synthesis rates of the different biopolymers. The specific rates of change of proteins and nucleic acids (except DNA) matched the dilution rate, both in the light and in the dark period. Carbohydrates were synthesized and stored at a very high rate during the photoperiod, and were metabolized for the provision of energy, and for biosynthesis of other biopolymers in the dark. Cell counts showed no evidence of phased synchrony, although this conclusion was contradicted by changes in DNA and pigments.