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1.
γ-Aminobutyric acid-α-ketoglutarate transaminase from is irreversibly inhibited by 4-aminohex-5-yhoic acid, a new structural analog of GABA. The fact that this inhibition requires the pyridoxal form of the holoenzyme, and the formation of a Michaelis complex is in support of a catalytic mechanism. The compound is also active and on the same enzyme from mammalian brain. 相似文献
2.
J C Shih 《Life sciences》1975,17(4):627-632
By means of a Sephadex-electrophoresis column, L-phenylalanine: pyruvate transaminase (PPT) was separated from L-phenylalanine: α-ketoglutarate transaminase (PKT) from rat liver. These enzymes differed in heat lability and in their inducibility by glucagon . PPT was heat-stable and was induced by chronic glucagon injection. On the other hand, PKT was heat-labile and was not induced by glucagon under the experimental conditions used. These studies provide evidence that distinct enzymes catalyze the transamination of phenylalanine with pyruvate or with α-ketoglutarate as the amino acceptor. 相似文献
3.
The extent of the hepatotoxic action of -hydroxy-2-acetylaminofluorene in the rat was determined by following changes in histochemistry, and the activities of glutamate-oxaloacetate transaminase (EC 2.6.1.1) and glutamate-pyruvate transaminase (EC 2.6.1.2) in serum. Administration of -hydroxy-2-acetylaminofluorene (120 μmol/kg i.v.) cased a periportal (zone I) necrosis which was accompanied by a large increase in glutamate-oxaloacetate transaminase and glutamate-pyruvate transaminase activity in serum. Treatment of rats with pentachlorophenol and 2, 6-dichloro-4-nitrophenol, known inhibitors of NO-sulfation, 45 min before the administration of -hydroxy-2-acetylaminofluorene, completely prevented the hepatotoxic effects of this carcinogenic hydroxamic acid. Therefore, it is concluded that NO-sulfation is responsible for the hepatotoxic action of -hydroxy-2-acetylaminofluorene. 相似文献
4.
The effect of hyperbaric oxygen on metabolism of the GABA shunt 总被引:1,自引:0,他引:1
Abstract— —The GABA-α-ketoglutarate transaminase pathway provides, in the brain, an alternative route for the conversion of α-ketoglutarate to succinate. In vitro experiments with rat brain homogenates and either [14C]GABA or [14C]α-ketoglutarate showed the percentage metabolism via the transaminase pathway to be about 17 per cent in air and 10 per cent oxygen at high pressure. Since the transaminase shunt was more sensitive to hyperbaric oxygen than the direct pathway, these results do not support the hypothesis of an alternative route operating under conditions of oxygen poisoning. 相似文献
5.
A series of 12α-hydroxy steroids with varying side chains was prepared, and their 24-hour acetylation yields were compared, l2α-Hydroxy-5β-pregnan-20-one () was prepared from 3α, 12α-diacetoxy-5β~pregnan-20-one () and also by side chain degradation of 12α-acetoxy-5β-cholanoic acid (). 21-Benzyl-5β-pregnan-12α-ol () was synthesized by hydrogenation of the 21-benzylidine derivative of ketone . 23-Pheny1-5β-norcholan-12α-ol () was obtained by the Grignard reaction of 2-phenyl-ethylmagnesium bromide and ketone , dehydration, hydrogenation and hydride reduction; a similar sequence produced 20-methyl-5β-pregnan-12α-ol (). The acetylation results (Table 11) imply that branching at C-20 may be more significant for 12α-hydroxyl reactivity than side chain length or type. An additional compound with an unbranched side chain, 21-nor-5β-cholan-12α-ol (), was synthesized by a Grignard reaction on the 21-bromo intermediate . Acetylation rates determined by glc indicate (Table 111) That compounds with unbranched side chains have 12α-hydroxyl groups about ten times as reactive as their analogs with 20-methyl groups. 相似文献
6.
The NADP+ specific glutamate dehydrogenase from wild-type forms a stable binary complex with NADPH. This can combine with L-glutamate, α-ketoglutarate or the substrate analogue D-glutamate to form ternary complexes which can be distinguished by their different fluorescence properties. The affinity of the enzyme for NADPH diminishes with increases in pH or ionic strength of the solution. Experimental data obtained using modified glutamate dehydrogenases from mutant strains of suggest that the reduced-coenzyme binding sites observed fluorimetrically are the same as those observed by enzyme kinetics. 相似文献
7.
A novel synthesis of 16α-hydroxy-4-androstene-3,17-dione (), 16α-hydroxy-4-androstene-3, 6,17-trione (), 17β-amino-5-androsten-3β-ol () and 17β-amino-4-androsten-3-one (14) is described. 16α-Bromoacetoxy-4-androstene-3, 17-dione (), 16α-bromoacetoxy-4-androstene-3, 6,17-trione () and 17β-bromoacetylamino-4-androsten-3-one () were synthesized as potentially selective irreversible inhibitors of androgen aromatases. 16α-Bromo-4-androstene-3,17-dione () and 16α-bromo-4-androstene-3, 6,17-trione () were converted to compounds and in 80–90% yield by controlled stereospecific hydrolysis using sodium hydroxide in aqueous pyridine. Reductive amination of 3β-hydroxy-5-androsten-17-one and 3-methoxy-3,5-androstadien-17-one () using ammonium acetate and sodium cyanohydridoborate (NaBH3CN) and a subsequent treatment with acid gave the amines and respectively, as a salt. The corresponding 17-imino compounds and were also isolated from the reaction mixtures when methanol was used as a solvent for the reaction. The 16α-hydroxyl compounds and and the 17β-amino compound were con- verted to the corresponding bromoacetyl derivatives, , , and , with bromoacetic acid and N,N'-dicyclohexylcarbodiimide. 相似文献
8.
Alanine formation by rat muscle homogenate 总被引:3,自引:0,他引:3
P T Ozand J T Tildon R A Wapnir M Cornblath 《Biochemical and biophysical research communications》1973,53(1):251-257
Rat hind leg muscle homogenates synthesized alanine at a rate of 1.06 μmoles/hr/gm for as long as 4 hours which is comparable to rates reported for perfusion experiments. Alanine synthesis by diaphragm and heart muscle was consistently less than 20% that of hind limb. Alanine formation was not enhanced by the addition of glucose, pyruvate or β-hydroxybutyrate nor was it decreased by proteolytic enzyme inhibitors. Homogenates were analyzed for concentrations of free amino acids and related intermediates (glutamate, α-ketoglutarate, lactate and pyruvate) with and without added NADH and lactic dehydrogenase. The results of these experiments suggest that the synthesis of alanine in hind limb muscle may be derived from sources other than pyruvate or proteolysis. 相似文献
9.
J Limón-Lason M Lara B Resendiz J Mora 《Biochemical and biophysical research communications》1977,78(4):1234-1240
The effect of the nitrogen and carbon sources in the regulation of gu tamine synthetase has been studied in fed-batch cultures of . The limitation of ammonium in an excess of the carbon source, leads to an accumulation of α-ketoglutarate and elevation of glutamine sy thetase. The limitation of sucrose in an excess of ammonium results in a decrease in glutamine synthetase activity. These results indicate that the carbon source exerts a positive control in the regulation of glutamine synthetase. 相似文献
10.
Akhil G. Jhingran R.C. Gupta Suprabhat Ray A.K. Agarwal M.M. Singh Nitya Anand 《Steroids》1983,42(6):627-634
The syntheses of (±) 2α,6β-diethyl-7α-ethynyl-3α-(-hydroxyphenyl)--bicyclo[4.3.0]nonan-7β-ol (), (±)2β,6β-diethyl-7α-ethynyl-3β-(-methoxyphenyl)--bicyclo[4.3.0]nonan-7β-ol () and (±) 2α,6β-diethyl-7α-ethynyl-3β-(-hydroxyphenyl)--bicyclo[4.3.0]nonan-7β-ol () and their derivatives, which are essentially B-seco-steroids having and geometries have been carried out. A study of their antiimplantation activities (AI) and receptor binding affinities (RBA) show that compounds are biologically most potent, followed by the corresponding and compounds. The most potent compound is active at 1 mg/kg in rats. Introduction of 7α-ethynyl group increases their AI activity; however, no significant effect on their RBA is observed. 相似文献
11.
The epididymis of adult rats metabolize 3H-testosterone by experiments . Thirty minutes after the injection of 100 μCi 3H-testosterone, some 10 per cent of the total radioactivity of the epididymis was found in the water-soluble fraction, whereas 90 per cent was found in the ether soluble fraction (free steroids). The free steroids were examined further and the following androgenic metabolites identified: (17β-hydroxy-4-androsten-3-one) 8, 9%, (4-androstene-3, 17-dione, 2,7%, (5α-androstane-3, 17-dione) 6,5%, (17β-hydroxy-5α-androstan-3-one) 47, 2%, (5α-androstane-3β, 17β-diol) 4, 4%, (5α-androstane-3α,17β-diol) 20, 8% and (3α-hydroxy-5α-androstan-3-one) 3,4%. The relative amount of each metabolite is given in per cent of total radioactivity in the ether soluble fraction. 相似文献
12.
Antoine Pilven Marie-Lise Thieulant Bernadette Ducouret Suzanne Sampérez Pierre Jouan 《Steroids》1976,28(3):349-358
The and metabolism of by the male rat anterior pituitary was studied. A rapid and intensive conversion of 5α-androstane-3α,17β-diol into 5α-dihydrotestosterone was demonstrated, since following a 30 min. incubation time, 73 % of the recovered radioactivity were constituted by 5α-dihydrotestosterone. Studies on the subcellular distribution of steroids showed that 5α-dihydrotestosterone was the main steroid recovered except from the 105,000 × g pellet. From and experiments it was concluded that the transformation of 5α-dihydrotestosterone into 5α-androstane-3α,17β-diol was a reversible process, and that this last steroid could exert its biological action mainly 5α-dihydrotestosterone. 相似文献
13.
Based on analysis of highly purified preparations of natural -factor and on the sequence recently reported by others, oligopeptides of the following structures were chemically synthesized by the solid phase method of Merrifield: N-Trp-His-Trp-Leu-Lys-Pro-Gly-G1N-Pro-Met-Tyr-C N-His-Trp-Leu-Lys-Pro-Gly-G1N-Pro-Met-Tyr-C Both synthetic species arrested cells in G1, inhibited their DNA synthesis, caused them to elongate markedly, and induced an increase in their adhesivity toward cells. Neither synthetic material caused any of these effects in cells or in diploids. 相似文献
14.
D2O-alanine exchange reactions catalyzed by alanine racemase and glutamic pyruvic transminase 总被引:1,自引:0,他引:1
NMR studies in D2O (>90%) reveal that Alanine Racemase (5.1.1.1.) from catalyzes the exchange of the α hydrogen of - and -alanine with D2O. Glutamic Pyruvic Transaminase (2.6.1.2.) and Glutamic Oxaloacetic Transaminase (2.6.1.1.) catalyze the exchange of α and β hydrogens of -alanine. The rates of exchange of α and β hydrogens appear to be of the same order of magnitude. The transaminase catalyzed exchange is enhanced by catalytic amounts of pyruvate. The side chain of -alanine is held more rigidly at the active site of transaminase so that the planar conjugated system can be extended to include the α and β carbons. A generalized mechanism is proposed for the action of pyridoxal phosphate dependent transaminases which extends Braunstein and Snell mechanism to include the structures which contribute to the labilization of β hydrogens of amino acids by the transaminases that have been studied. 相似文献
15.
The effects of 19-hydroxy-prostaglandins (19-OH-PGs) were tested on the rabbit oviduct and uterus and on the rhesus monkey () uterus. The 19-OH-PGEs suppressed spontaneous oviductal and uterine activity in the rabbit. The qualitative effect on the rabbit oviduct of 19-OH-PGEs was similar to that of PGE2. However, the typical response of the rabbit uterus to PGE2 was an increase in muscle activity. With regard to the rabbit oviduct, 19(R)-OH-PGE2 was as potent as PGE2, but 19(S)-OH-PGE2 was approximately as potent as PGE2. Based on the dose of 19-OH-PGEs usually required to cause a minimal suppression and the dose of PGE2 required to cause a minimal stimulation of rabbit uterine activity, 19(R)-OH-PGE2 was twice as potent as PGE2 while 19(S)-OH-PGE2 was as potent as PGE2. Stimulatory effects on the rabbit oviduct and uterus were observed following administration of 19-OH-PGEs and PGF2α. The potency on the rabbit oviduct of 19(S)-OH-PGF2α was about to that of PGF2α; the potency of 19(R)-OH-PGF2α was about to that of PGF2α. Both 19-OH-PGFs were approximately to as potent as PGF2α on the rabbit uterus. At the doses tested 19-OH-PGFs were inactive on the monkey uterus. Thus, these compounds are at least as active as PGF2α. In contrast, 19(R)-OH-PGE2 had approximately the same potency as PGE2 in stimulating monkey uterine activity; but 19(S)-OH-PGE2 was approximately as potent as PGE2. 相似文献
16.
The presence of glutamate synthase in the green algae var. has been demonstrated using a whole cell assay as well as cell free extracts. The assay is complicated by the presence of glutamine (amino): α-oxoglutarate transaminase, but this enzyme can be inhibited by amino oxyacetate. The rates of glutamate synthase activity are sufficient to account for the known rates of nitrate assimilation to occur via the glutamine synthetase/glutamate synthase pathway. 相似文献
17.
Y. Chandra Sekharudu V.S.R. Rao 《International journal of biological macromolecules》1984,6(6):337-347
The possible modes of binding for , , , and to concanavalin A have been investigated using theoretical methods. All these sugars, except , reach the active site of concanavalin A with a highly restricted number of binding orientations. Present investigations suggest that the failure of to bind to concanavalin A is not so much due to steric factors as to repulsive electrostatic interactions. can bind to concanavalin A in one mode whereas the other sugars can bind in more than one mode. The high potency of over is mainly due to the possibility of hydrophobic interactions of the α-methoxy group with Leu(99) or Tyr(100) and also due to the possibility of formation of better and more hydrogen bonds with the protein. A comparison of these data with those for the d-glucopyranosides suggests that the change of the hydroxyl at the C-2 atom from equatorial to axial orientation increases the stereochemically allowed region as well as the possible binding modes. From these studies it is also suggested that the overall shape of the oligosaccharides rather than the terminal or internal mannose alone affects the binding potency of saccharides to concanavalin A. 相似文献
18.
The Dieckmann condensation of dimethyl 3, 4--5α-cholestan-3, 4-dioate (), using sodium methoxide in benzene under reflux for two hours, is shown to give 2α-carbomethoxy-A-nor-5α-cholestan-3-one (). Confirmation of the stereochemistry of the β-keto ester was obtained through its sodium borohydride reduction product, 2α-carbomethoxy-A-nor-5α-cholestan-3β-ol (). 相似文献
19.
Controlled alkaline hydrolysis of 16α-bromo-17-keto steroids , and with potassium carbonate and tetra-n-butylammonium hydroxide (n-Bu4NOH) and synthesis of 2α-hydroxy-3-ones , and by the controlled hydrolysis of the corresponding 2α-bromo-3-ones , and are described. Treatm carbonate in aqueous acetone or with n-Bu4NOH in aqueous dimethylformamide (DMF) gave 16α-hydroxy-17-ones , and in 85–90% yield, respectively. 2α-Hydroxy-3-ones , and were obtained by hydrolysis of the corresponding bromoketones , and in high yields using the above conditions or sodium hydroxide in pyridine or DMF, respectively. Deuterium labeling experiments suggested that equilibration between the 2α-bromoketone and the 2β-bromo isomer precedes the formation of the ketol in which the true intermediate might be the 2β-isomer . However, rearranged androstane derivatives, 3β-hydroxy-2-ones and , were stereoselectively obtained by treatment of the bromoketones and with an excess amount of sodium hydroxide. 相似文献
20.
Bojan Hamlin Jennings Sharon Martin Boudreau Beverly Braasch Cheryl Garganta 《Steroids》1982,39(4):371-380
Both the 5α, 6α- and 5β, 6β-dichloromethylene adducts ( and ) of 3β-acetoxy-5-androsten-17-one () are produced when the latter is exposed to dichlorocarbene generated from chloroform and base by Phase Transfer Catalysis using ultrasound as a means of agitation. The 1H NMR substituent effects of 5α, 6α- and 5β, 6β-dichloromethylene on the angular methyl groups (Zürcher values) are given. The 13C NMR spectra for both compounds are presented and discussed. 相似文献