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51.
Studies were carried out on glutamate dehydrogenase (GDH, EC 1.4.1.2) isolated from the SB1 and SB3 soybean (Glyciene max L. cv. Mandarin) cell cultures. The NAD(H) dependent enzyme from SB1 and SB3 cells was purified to homogeneity, and that from the SB3 cells studied in detail. It was shown to be activated by calcium. The molecular weight of the native enzyme was found to be 263 000 ± 12 000. The molecular weight of the subunits was shown to be 41 000 ± 2000, which indicates that the enzyme has a hexameric structure. Anti-GDH antibodies were produced in rabbits, to GDH purified to homogeneity from both cell cultures. Each antibody preparation reacted with the purified enzyme produced from either cell culture. Antibodies to GDH from SB3 cells were utilized to study the apparent induction of GDH, which occurs when these cells are grown in a medium with ammonium ions as the sole nitrogen source. The increase in GDH activity was shown to be due to de-novo protein synthesis. The anti-SB3-GDH antibody preparation was also tested for cross reactivity with crude GDH preparations from a number of plant sources, and purified GDH from a number of other organisms. The antibody was shown to cross react with a number of the GDH preparations. 相似文献
52.
Thomas A. Churchill Kenneth B. Storey 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(4):461-472
Summary The course of glycerol biosynthesis, initiated by exposure to –4°C, was monitored in larvae of the goldenrod gall moth,Epiblema scudderiana, and accompanying changes in the levels of intermediates of glycolysis, adenylates, glycogen, glucose, fructose-2,6-bisphosphate, and fermentative end products were characterized. Production of cryoprotectant was initiated within 6 h after a switch from +16° to –4°C, with halfmaximal levels reached in 30 h and maximal content, 450–500 mol/g wet weight, achieved after 4 days. Changes in the levels of intermediates of the synthetic pathway within 2 h at –4°C indicated that the regulatory sites involved glycogen phosphorylase, phosphofructokinase, and glycerol-3-phosphatase. A rapid increase in fructose-2,6-bisphosphate, an activator of phosphofructokinase and inhibitor of fructose-1,6-bisphosphatase, appeared to have a role in maintaining flux in the direction of glycerol biosynthesis. Analysis of metabolite changes as glycerol production slowed suggested that the inhibitory restriction of the regulatory enzymes was slightly out of phase. Inhibition at the glycerol-3-phosphatase locus apparently occurred first and resulted in a build-up of glycolytic intermediates and an overflow accumulation of glucose. Glucose inhibition of phosphorylase, stimulating the conversion of the activea to the inactiveb forms, appears to be the mechanism that shuts off phosphorylase function, counteracting the effects of low temperature that are the basis of the initial enzyme activation. Equivalent experiments carried out under a nitrogen gas atmosphere suggested that the metabolic make-up of the larvae in autumn is one that obligately routes carbohydrate flux through the hexose monophosphate shunt. The consequence of this is that fermentative ATP production during anoxia is linked to the accumulation of large amounts of glycerol as the only means of maintaining redox balance.Abbreviations
G6P
glucose-6-phosphate
-
F6P
fructose-6-phosphate
-
F1, 6P
fructose-1,6-bisphosphate
-
F2,6P
2
fructose-2,6-bisphosphate
-
G3P
grycerol-3-phosphate
-
DHAP
dinydroxyacetonephosphate
-
GAP
glyceraldehyde-3-phosphate
-
PEP
phosphoenolpyruvate
-
PFK
phosphofructokinase
-
FBPase
fructose-1,6-bisphosphatase
-
PK
pyruvate kinase 相似文献
53.
Summary It is difficult to distinguish between Goormaghtigh cells (G-cells) and media cells of the glomerular arterioles at the border of the Goormaghtigh cell field. Consequently, it has been unclear whether renin-positive G-cells are normally present and also whether renin-producing cells are recruited from the pool of renin-negative G-cells upon stimulation of the renin-angiotensin system (RAS). In the present study, immunohistochemical and electron-microscopic experiments have been carried out on serially sectioned kidney biopsies from four patients with pseudo-Bartter syndrome. The results strongly suggest that with longlasting stimulation of the RAS all renin-negative (secretory resting) G-cells are ultimately converted into renin-producing granular cells.Synonymous with extraglomerular mesangial cells 相似文献
54.
55.
Acetyl-l-carnitine as a precursor of acetylcholine 总被引:2,自引:0,他引:2
Synthesis of [3H]acetylcholine from [3H]acetyl-l-carnitine was demonstrated in vitro by coupling the enzyme systems choline acetyltransferase and carnitine acetyltransferase. Likewise, both [3H] and [14C] labeled acetylcholine were produced when [3H]acetyl-l-carnitine andd-[U-14C] glucose were incubated with synaptosomal membrane preparations from rat brain. Transfer of the acetyl moiety from acetyl-l-carnitine to acetylcholine was dependent on concentration of acetyl-l-carnitine and required the presence of coenzyme A, which is normally produced as an inhibitory product of choline acetyltransferase. These results provide further evidence for a role of mitochondrial carnitine acetyltransferase in facilitating transfer of acetyl groups across mitochondrial membranes, thus regulating the availability in the cytoplasm of acetyl-CoA, a substrate of choline acetyltransferase. They are also consistent with a possible utility of acetyl-l-carnitine in the treatment of age-related cholinergic deficits. 相似文献
56.
A stable period length is a characteristic property of circadian oscillations. The question about whether higher frequency oscillators (0.5-8 hr) contribute to or establish the stable circadian periodicity cannot be answered at present. A sequential coupling of quantal subcycles appears possible on the basis of known “ultradian” oscillations. There is, however, no supporting evidence for such a concept. Phase response curves of the circadian clock derived from various perturbing pulses allow qualitative conclusions concerning the perturbed clock process. Deductions from computer simulations also allow conclusions about the phase of this oscillatory process.
The distinction between processes (a) essential to the clock mechanism, (b) maintaining and controlling the clock (inputs) and (c) depending on the clock (outputs) on the basis of “oscillatory” and “change of φ or τ after perturbation” seems to be useful but not stringent. Protein synthesis may be an essential or input process. Oscillatory changes of this process may be due to periodic translational control or RNA-supply. Circadian changes in protein concentration and/or activity may depend on periodic synthesis, proteolysis, covalent modifications or aggregations. Specific essential proteins have not been identified conclusively. The large overlap between the group of agents and treatments that phase shift the clock and the group that induces stress proteins suggest that the latter may play a role in the controlling (input) or essential domain.
The role of membranes in the clock mechanism is not clear: concepts assuming an essential function are based on circumstantial evidence. The membrane potential as well as Ca2+ may be involved in either input or essential function. Ca2+ -calmodulin may also be important as concluded from inhibitor experiments. It is tempting to assume that a calmodulin-dependent kinase is part of a periodic protein phosphorylation process, yet it is not clear whether the periodic protein phosphorylation that has been observed is essential or is just another output process. 相似文献
The distinction between processes (a) essential to the clock mechanism, (b) maintaining and controlling the clock (inputs) and (c) depending on the clock (outputs) on the basis of “oscillatory” and “change of φ or τ after perturbation” seems to be useful but not stringent. Protein synthesis may be an essential or input process. Oscillatory changes of this process may be due to periodic translational control or RNA-supply. Circadian changes in protein concentration and/or activity may depend on periodic synthesis, proteolysis, covalent modifications or aggregations. Specific essential proteins have not been identified conclusively. The large overlap between the group of agents and treatments that phase shift the clock and the group that induces stress proteins suggest that the latter may play a role in the controlling (input) or essential domain.
The role of membranes in the clock mechanism is not clear: concepts assuming an essential function are based on circumstantial evidence. The membrane potential as well as Ca2+ may be involved in either input or essential function. Ca2+ -calmodulin may also be important as concluded from inhibitor experiments. It is tempting to assume that a calmodulin-dependent kinase is part of a periodic protein phosphorylation process, yet it is not clear whether the periodic protein phosphorylation that has been observed is essential or is just another output process. 相似文献
57.
Generation of potential structures for the G-domain of chloroplast EF-Tu using comparative molecular modeling 总被引:2,自引:0,他引:2
Comparative molecular modeling has been used to generate several possible structures for the G-domain of chloroplast elongation factor Tu (EF-Tu(chl)) based on the crystallographic data of the homologous E. coli protein. EF-Tu(chl) contains a 10 amino acid insertion not present in the E. coli protein and this region has been modeled based on its predicted secondary structure. The insertion appears to lie on the surface of the protein. Its orientation could not be determined unequivocally but several likely structures for the nucleotide binding domain of EF-Tu(chl) have been developed. The effects of the presence of water in the Mg2+ coordination sphere and of the protonation state of the GDP ligand on the conformation of the guanine nucleotide binding site have been examined. Relative binding constants of several guanine nucleotide analogs for EF-Tu(chl) have been obtained. The interactions between EF-Tu(chl) and GDP predicted to be important by the models that have been developed are discussed in relation to the nucleotide binding properties of this factor and to the interactions proposed to be important in the binding of guanine nucleotides to related proteins. 相似文献
58.
Groups of CBA mice were administered [35S] methionine (1 mCi/mouse). Non-histone proteins, H1 and H10 histones and nucleosomal core histones were isolated from different issues by selective extractions. The measurements of radioactivity of individual bands and autoradiography of dry gels were used to identify methionine-containing and methionine-free histone variants. H1A and H1B histone variants extracted with 5% perchloric acid were methionine-free. However, minor sub-fractions of these histones which are more tightly bound to DNA (and which can be extracted only with 0.25 N HC1) contained [35S] methionine and did show a higher specific activity than methionine-containing nucleosomal hitones. Cyanogen Bromide reaction which destroys non-histone proteins and methionine-containing nucleosomal histones removes radioactivity but does not alter the position of methionine-containing H1 minor bands. This indicates that the radioactive methionine occupies only the N-terminus of the H1 molecules. It is suggested that this methionine is an uncleaved initiator methionine. The presence of these methionine-containing minor H1 subfractions varies in different tissues. 相似文献
59.
R. Ayola D. F. Condorelli N. Ragusa M. Renis M. Alberghina A. M. Giuffrida Stella Abel Lajtha 《Neurochemical research》1988,13(4):337-342
In vivo protein synthesis rates in various brain regions (cerebral cortex, cerebellum, hippocampus, hypothalamus, and striatum) of 4-, 12-, and 24-month-old rats were examined after injection of a flooding dose of labeled valine. The incorporation of labeled valine into proteins of mitochondrial, microsomal, and cytosolic fractions from cerebral cortex and cerebellum was also measured. At all ages examined, the incorporation rate was 0.5% per hour in cerebral cortex, cerebellum, hippocampus, and hypothalamus and 0.4% per hour in striatum. Of the subcellular fractions examined, the microsomal proteins were synthesized at the highest rate, followed by cytosolic and mitochondrial proteins. The results obtained indicate that the average synthesis rate of proteins in the various brain regions and subcellular fractions examined is fairly constant and is not significantly altered in the 4 to 24-month period of life of rats.A preliminary report of these results was previously presented at: WFN-ESN Joint Meeting on: Cerebral Metabolism in Aging and Neurological Disorders, Baden, August 28–31, 1986. 相似文献
60.