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1.
The turnover rate of tubulin in rat brain was determined from the decay in specific radioactivity of the protein after pulse-labeling. When precursors were administered by a parenteral route, the shortest half-life, 9.8 days, was obtained with [14C]NaHCO3; the longer half-lives obtained with [U-14C]glucose or [4,5-3H]leucine suggest significant reutilization of label. Furthermore, with leucine as precursor maximal specific radioactivity of tubulin was not obtained until eight days after administration of label. Labeling and decay kinetics obtained with [4,5-3H]leucine were markedly different when the isotope was administered directly into the lateral ventricle. The difference between the turnover rates of the -α and β subunits of tubulin purified by means of high resolution polyacrylamide gel electrophoresis was not statistically significant. A half-life for tubulin of 6.2 days was measured by continuous intravenous infusion of [U-14C]tyrosine. 相似文献
2.
Abstract— Protein turnover in rat brain was measured over a period of 30 days by following the decay in specific radioactivity of acidic amino acids in proteins labelled by a single intraperitoneal injection of [14C]NaHCO3. Two major populations of brain proteins can be identified from the resultant non-linear decay curve—one with an average half-life of 4 days and another with an average half-life of 12 days. The half-lives of total brain, mitochondrial, microsomal and soluble proteins determined over a period of 5 days were 3.4, 5.8, 2.8, and 2.6 days, respectively. Turnover of these same brain subcellular fractions was also measured by continuous infusion of [14C]tyrosine. The estimated half-lives were in close agreement with those obtained from the 5 day measurement of radioactive decay following a pulse label of [14C]NaHCO3. 相似文献
3.
THE INFLUENCE OF PORTOCAVAL ANASTOMOSIS ON THE METABOLISM OF LABELLED OCTANOATE, BUTYRATE AND LEUCINE IN RAT BRAIN 总被引:6,自引:6,他引:0
Rats were given a portocaval anastomosis and 3 weeks later, when the only ultrastructural change in the CNS is watery swelling of astrocytes, several aspects of brain metabolism were studied. The uptake of leucine by the brain, its incorporation into protein and its oxidation were followed after the simultaneous injection of a mixture of L-[114C]leucine and L-[4,5-3H]leucine. The concentration of leucine in blood was lowered in the operated animals whereas in brain it was increased. The specific radioactivity of leucine in the brain was comparable to values in control animals and there was no evidence of a decrease in incorporation of [1-14C]leucine into brain proteins over the short experimental time period studied. The only difference from the controls in the oxidation of [4,5-3H]leucine was a greater accumulation in glutamine. The amount of glutamine in the brains of the operated animals had increased 4-fold at the time of the metabolic studies. From dual-labelled experiments in which a mixture containing [1-14C]butyrate and L-[4,5-3H]leucine was injected intravenously, it was shown that, in both control and operated animals, the pools of brain glutamate and glutamine labelled from butyrate were metabolically distinct from those labelled from leucine. The total radioactivity appearing in brain from [1-14C]butyrate was markedly reduced in operated animals, but the radioactivity from L-[4,5-3H]leucine was not. The metabolism of [1-14C]octanoate was compared with that of [1-14C]butyrate. In control animals the labelling of metabolites was almost identical with either precursor. In operated animals there was no reduction in the uptake of [1-14C]octanoate into the brain. There was evidence that the size of the glutamine pool labelled, relative to glutamate, was increased but that it had a slower fractional turnover coefficient. A link between astroglial changes and an impairment to the carrier mechanism for transport of short chain monocarboxylic acids across the blood-brain barrier is suggested. 相似文献
4.
Haem a, cytochrome c and total protein turnover in mitochondria from rat heart and liver 总被引:11,自引:9,他引:2
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Haem a and cytochrome c were isotopically labelled in mitochondria from rat heart and liver after injection of delta-amino[2,3-(3)H(2)]laevulate, a specific haem precursor. [guanido-(14)C]Arginine or l-[4,5-(3)H(2)]leucine were used to label mitochondrial proteins. Half-lives were measured from biological decay in vivo and were similar (5.5-6.2 days) for haem a, cytochrome c and [(14)C]arginine-labelled proteins. Labelling of hepatic mitochondrial proteins with [(3)H(2)]leucine resulted in a prolonged apparent half-life. 相似文献
5.
Abstract— The oxidation of l -[U-14C]leucine and l -[l-14C]leucine at varying concentrations from 0.1 to 5mM to CO2 and the incorporation into cerebral lipids and proteins by brain slices from 1-week old rats were markedly stimulated by glucose. Although the addition of S mM-dl -3-hydroxybutyrate had no effect on the metabolism of [U-14C]leucine by brain slices from suckling rats, the stimulatory effects of glucose on the metabolism of l -[U-14C]leucine were markedly reduced in the presence of dl -3-hydroxybutyrate. The stimulatory effect of glucose on leucine oxidation was, however, not observed in adult rat brain. Furthermore, the incorporation of leucine-carbon into cerebral lipids and proteins was also very low in the adult brain. The incorporation of l -[U-14C]leucine into cerebral lipids by cortex slices was higher during the first 2 postnatal weeks, which then declined to the adult level. During this time span, the oxidation of l -[U-14C]leucine to CO2 remained relatively unchanged. The incorporation in vivo of D-3-hydroxy[3-14C]butyrate into cerebral lipids was markedly decreased by acute hyperleucinemia induced by injecting leucine into 9-day old rats. In in vitro experiments, 5 mM-leucine had no effect on the oxidation of [U-14C]glucose to CO2 or its incorporation into lipids by brain slices from 1-week old rats. However, 5 mM-leucine inhibited the oxidation of d -3-hydroxy-[3-14C]butyrate, [3-14C]acetoacetate and [1-14C]acetate to CO2 by brain slices, but their incorporation into cerebral lipids was not affected by leucine. In contrast 2-oxo-4-methylvalerate, a deaminated metabolite of leucine, markedly inhibited both the oxidation to CO2 and the incorporation into lipids of labelled glucose, ketone bodies and acetate by cortex slices from 1-week old rats. These findings suggest that the reduction in the incorporation in vivo of d -3-hydroxy[3-14C]butyrate into cerebral lipids in rats injected with leucine is most likely caused by 2-oxo-4-methylvalerate formed from leucine. Since the concentrations of leucine and 2-oxo-4-methylvalerate in plasma of untreated patients with maple-syrup urine disease are markedly elevated, our findings are compatible with the possibility that an alteration in the metabolism of glucose and ketone bodies in the brain may contribute to the pathophysiology of this disease. 相似文献
6.
Normand Marceau Julien Deschênes Jacques Landry 《Archives of biochemistry and biophysics》1980,199(2):384-392
The average decay rates (half-lives) of mixed glycoproteins were measured using double isotopes of fucose and glucosamine and compared to those of mixed overall proteins measured with leucine and NaH14CO3 in whole homogenates and plasma membranes from normal and regenerating rat livers. A large reutilization of leucine was observed under both normal and regenerating conditions. Fucose seems to be recycling most predominantly in regenerating liver, whereas glucosamine was found to be very little if not at all reutilized under both conditions. Comparison of the results obtained with NaH14CO3 and glucosamine demonstrated that glycoproteins from normal liver homogenate are degraded at a faster rate than mixed proteins. Contrary to that of mixed proteins, the half-life of glycoproteins remains unchanged during liver regeneration, and the use of glucosamine revealed that the degradation of plasma membrane glycoproteins is identical to that found in whole homogenate under both normal and regenerating conditions. Finally, the relative degradation rates of fractionated plasma membrane proteins and glycoproteins were evaluated under the same conditions. During liver regeneration some readjustments are observed in the relative degradation rates of individual species which suggest that the synthesis and degradation of the various surface membrane glycoproteins proceed at rates that are controlled independently. 相似文献
7.
—The incorporation of [4,5-3H]lysine and [1-14C]leucine into the proteins of subcellular fractions of mouse brain was examined following a single electroconvulsive shock (ECS) or following cycloheximide injections. When the [3H]lysine was injected intraperitoneally immediately after the ECS the incorporation into total brain proteins was decreased by more than 50% as compared to sham controls. The proportion of lysine incorporated into the microsomal fraction was increased, but no changes were observed in the other subcellular fractions including the synaptosomal fraction. With extended pulses administered at various times after the ECS there was no change in total incorporation nor were selective effects seen in any subcellular fractions. With intracranial injections of both [3H]lysine and [14C]leucine the decreased incorporation caused by ECS was not observed, neither were there selective changes in any subcellular fraction. This lack of inhibition occurred because the intracranial injection itself severely inhibited [3H]lysine incorporation. Cycloheximide (30 mg/kg) which depressed [3H]lysine incorporation into brain proteins by 84% caused a selective depression of the incorporation into the cell-sap fraction and selective elevations into the microsomal and synaptosomal fractions. Similar changes were seen with a higher (amnestic) dose of cycloheximide (150 mg/kg) which inhibited incorporation by 94%. These data are interpreted in terms of the diverse mechanisms by which ECS and cycloheximide inhibit protein synthesis. 相似文献
8.
Biosynthesis of myelin proteins in vitro 总被引:3,自引:3,他引:0
Abstract— The rates of uptake of DL-[1-14C]leucine into the three classes of protein in myelin isolated from slices of rat brain and spinal cord were determined. Basic protein exhibited the slowest rate of uptake; chloroform-methanol-soluble proteolipid protein exhibited intermediate rates and the insoluble protein had the most active uptake. All myelin proteins were less active than the mixture of proteins derived from the non-myelin fraction. Cyclohexi-mide (10?3 M) and choramphenicol (5 × 10?3 M) inhibited the incorporation of [1-14C]leucine into brain proteins by as much as 95 per cent. γ-Aminobutyric acid had no effect on the system. Chloramphenicol also inhibited the uptake of [1-14C]acetate into myelin lipids, but cycloheximide did not affect lipid synthesis. These effects were observed on both 35-day-oldand 18-month-old rats, but the biosynthetic activity was far less in myelin from the older rats. The results are discussed in relation to the structure of myelin. It is suggested that the data best fit models in which lipid and protein are in separate phases in the membrane. 相似文献
9.
dos Santos Fagundes I Rotta LN Schweigert ID Valle SC de Oliveira KR Huth Krüger A Souza KB Souza DO Perr ML 《Neurochemical research》2001,26(3):245-249
We have investigated the glycine, serine and leucine metabolism in slices of various rat brain regions of 14-day-old or adult rats, using [1-14C]glycine, [2-14C]glycine, L-[3-14C]serine and L-[U-14C]leucine. We showed that the [1-14C]glycine oxidation to CO2 in all regions studied occurs almost exclusively through its cleavage system (GCS) in brains of both 14-day-old and adults rats. In 14-day-old rats, the highest oxidation of [1-14C]glycine was in cerebellum and the lowest in medulla oblongata. In these animals, the L-[U-14C]leucine oxidation was lower than the [1-14C]glycine oxidation, except in medulla oblongata where both oxidations were the same. Serine was the amino acid that showed lowest oxidation to CO2 in all structure studied. In adult rats brains, the highest oxidation of [1-14C]glycine was in cerebral cortex and the lowest in medulla oblongata. We have not seen difference in the lipid synthesis from both glycine labeled, neither in 14-day-old rats nor in adult ones, indicating that the lipids formed from glycine were not neutral. Lipid synthesis from serine was significantly high than lipid synthesis and from all other amino acids studied in all studied structures. Protein synthesis from L-[U-14C]leucine was significantly higher than that from glycine in all regions and ages studied. 相似文献
10.
The synthesis and decay of histone fractions and of deoxyribonucleic acid in the developing avian brain
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Stephen C. Bondy 《The Biochemical journal》1971,123(3):465-469
1. The turnover of cerebral histones and DNA after injection of [4,5-(3)H]leucine or [methyl-3-(3)H]thymidine, respectively, was studied in the developing chick. 2. Chromatin was prepared from chick nuclei that had been purified by centrifugation through 1.9m-sucrose. 3. Nuclear proteins were fractionated into three major histone classes, F1 (lysine-rich), F2(b) (slightly lysine-rich) and [F3+F2(a)] (arginine-rich), and a non-histone protein residue. 4. The proportions of the histone classes remained constant throughout the period of development studied. 5. All histone fractions decayed at a similar rate, initially with a half-life of around 5 days, later with a half-life of 19 days. 6. Non-histone proteins from chromatin decayed in a heterogeneous manner with a wide range of half-lives. 7. Short-term labelling studies showed that all histone fractions were synthesized at the same rate. 8. Some non-histone proteins were very rapidly synthesized relative to histones. 9. DNA had a longer half-life than any histone fraction studied. A biphasic exponential decay curve with half-lives of 23 and 50 days was found. 10. It was concluded that the turnover of histones can occur independently of that of DNA and that different histone classes have similar rates of synthesis and decay. 相似文献
11.
TURNOVER OF PHOSPHATIDYLCHOLINE IN MICROSOMES AND MYELIN IN BRAINS OF YOUNG AND ADULT RATS 总被引:2,自引:1,他引:1
We have tested the hypothesis that the turnover of phosphatidylcholine in subcellular fractions of rat brain is a function of the age at which this lipid is deposited. Rats, 60 days of age, were injected intracranially with [2-3H]glycerol and either [methyl-14C]choline (to label the base moiety) or [U-14C]glucose (to label acyl moieties). Littermates were killed up to 90 days after injection and brain microsomes and myelin isolated. Lipids were extracted and the phosphatidylcholine was isolated by 2-dimensional TLC and hydrolyzed to its constituent moieties. The 3H in the glycerol backbone and 14C in the choline or acyl residues was quantitated. The microsomal and myelin 3H/14C ratios decreased with time with either set of precursors, indicating that labeled choline and acyl moieties were reutilized more efficiently than the glycerol backbone. The various precursors exhibited first order decay curves with half-lives for the glycerol backbone of 6 and 11 days for the microsomal and myelin fractions respectively. These results contrast with those previously obtained with identical experimental procedures when 17-day-old animals were injected. In that study, although much of the phosphatidylcholine turned over rapidly as for the older animals, by 2 weeks after injection most of the remaining phosphatidylcholine was turning over more slowly with a half-life of 13 and 25 days for microsomes and myelin respectively (Miller et al., 1977). The base and acyl moieties also had a corresponding shorter half-life in older animals relative to the slow turnover phase in younger rats. 相似文献
12.
J. A. Burdman 《Journal of neurochemistry》1970,17(11):1555-1562
Purified neuronal and glial nuclei were separated from rat brain cells. The fraction rich in neuronal nuclei contained 68 ± 9 per cent neuronal nuclei and the fraction rich in glial nuclei contained 89 ± 6 per cent glial nuclei. The fraction rich in neuronal nuclei isolated from cells of adult rat brain incorporated l -[4,5-3H]leucine into TCA-insoluble material at a rate comparable to those of the microsomal and the soluble fractions of the brain, and at a much higher rate than the fraction rich in glial nuclei. The proteins soluble in buffered-saline, the acid-soluble deoxyribonucleoproteins, and the residual proteins of the neuronal nuclei are apparently the proteins which account for the higher specific activity of neuronal proteins compared with glial nuclear proteins. In liver and kidney, the incorporation of [3H]leucine into nuclear proteins was lower than into other subcellular fractions from the same organs. 相似文献
13.
A procedure is described for the isolation from the phototrophic procaryole Anacystis nidulans of [U-14C]-labelled glycogen, with high specific radioactivity,formed when NaH14CO3 was added to non-dividing cells that continued to photoassimilate CO2. [U-14C]-Labelled glycogen was then treated with isoamylase (EC 3.2.1.68), isoamylase plus beta-amylase (EC 3.2.1.2), or glucoamylase (EC 3.2.1.3) to give [U-14C]-labelled maltosaccharides, maltose-U-14C, or d-glucose-U-14C, respectively. 相似文献
14.
Patrick A. Sinnett-Smith Richard G. Vernon R. John Mayer 《Biochimica et Biophysica Acta (BBA)/General Subjects》1982,714(1):58-64
1. The relative rates of synthesis of fatty acid synthetase and the pyruvate dehydrogenase complex were measured in adipose tissue in virgin, late pregnant and early lactating rats after injection of l-[2,3-3H]alanine. The relative rate of synthesis of fatty acid synthetase decreased approximately 4-fold between 2 days prepartum and 2 days postpartum. The relative rate of synthesis of the pyruvate dehydrogenase complex did not change. 2. The fractional rate of total adipose tissue protein synthesis was measured by constant infusion with l-[U-14C]tyrosine. Total protein synthesis did not differ in virgin and 2-day lactating rats. The half-life of adipose tissue protein in virginn rats determined by decay of 14C label from protein after injection of NaH14CO3 was 86.9 ± 6.7 h. This is in close agreement witht the half-life (82.5 ± 20 h) calculated from the fractional rate of protein synthesis determined by the constant infusion method. 相似文献
15.
Keiji Tanaka Naohiko Ikegaki Akira Ichihara 《Archives of biochemistry and biophysics》1981,208(1):296-304
Addition of pepstatin, an inhibitor of acid protease, to 2-day cultures of rat hepatocytes rapidly inhibited the activity to hydrolyze hemoglobin (Hb), but did not affect the activity to hydrolyze α-N-benzoyl-dl-arginine-β-naphthylamide (BANA). On the other hand, addition of leupeptin, an inhibitor of thiol protease, inhibited the activity of BANA hydrolase and caused a sixfold increase in the activity of Hb hydrolase within 1 day. Neither protease inhibitor affected the rate of protein synthesis. Release of amino acids from hepatocytes into Hanks' salt solution was measured by the ninhydrin method. Pepstatin inhibited the release only 15% within 2 days, but leupeptin inhibited it 65% within 10 h. These two inhibitors had additive inhibitory effects on the release, suggesting that they inhibit the degradations of different groups of proteins. The inhibitory effect of leupeptin gradually decreased after 10 h, which is consistent with the observed induction of a protease activity mentioned above. A preferential involvement of leupeptin-sensitive protease in the degradation of proteins with longer half-lives was suggested from studies on [14C]leucine release from hepatocytes prelabeled for 30 h. On the other hand, the two inhibitors had similar effects on the release of [14C]leucine from hepatocytes labeled for only 1 h. Their inhibitory effects were again additive, but there was no reduction in the inhibition by leupeptin on prolonged incubation, suggesting that proteins with short half-lives were not substrates for the induced protease. These results suggest that in hepatocytes, proteins with longer half-lives are degraded more by cathepsin B than by cathepsin D, while those with short half-lives are degraded equally by these two proteases. 相似文献
16.
The incorporation of [methyl-3H]thymidine into DNA, of [5-3H]uridine into RNA, and of [1-14C]leucine into proteins of cerebral hemispheres, cerebellum, and brainstem of guinea pigs after 80 hr of hypoxic treatment was measured. Both in vivo (intraventricular administration of labeled precursors) and in vitro (tissue slices incubation) experiments were performed. The labeling of macromolecules extracted from the various subcellular fractions of the above-mentioned brain regions was also determined. After hypoxic treatment the incorporation of the labeled precursors into DNA, RNA, and proteins was impaired to a different extent in the three brain regions and in the various subcellular fractions examined; DNA and RNA labeling in cerebellar mitochondria and protein labeling in microsomes of the three brain regions examined were particularly affected. 相似文献
17.
PROVENANCE OF THE ACETYL GROUP OF ACETYLCHOLINE AND COMPARTMENTATION OF ACETYL-CoA AND KREBS CYCLE INTERMEDIATES IN THE BRAIN IN VIVO 总被引:16,自引:14,他引:2
—The origin of the acetyl group in acetyl-CoA which is used for the synthesis of ACh in the brain and the relationship of the cholinergic nerve endings to the biochemically defined cerebral compartments of the Krebs cycle intermediates and amino acids were studied by comparing the transfer of radioactivity from intracisternally injected labelled precursors into the acetyl moiety of ACh, glutamate, glutamine, ‘citrate’(= citrate +cis-aconitate + isocitrate), and lipids in the brain of rats. The substrates used for injections were [1-14C]acetate, [2-14C]acetate, [4-14C]acetoacetate, [1-14C]butyrate, [1, 5-14C]citrate, [2-14C]glucose, [5-14C]glutamate, 3-hydroxy[3-14C]butyrate, [2-14C]lactate, [U-14C]leucine, [2-14C]pyruvate and [3H]acetylaspartate. The highest specific radioactivity of the acetyl group of ACh was observed 4 min after the injection of [2-14C]pyruvate. The contribution of pyruvate, lactate and glucose to the biosynthesis of ACh is considerably higher than the contribution of acetoacetate, 3-hydroxybutyrate and acetate; that of citrate and leucine is very low. No incorporation of label from [5-14C]glutamate into ACh was observed. Pyruvate appears to be the most important precursor of the acetyl group of ACh. The incorporation of label from [1, 5-14C]citrate into ACh was very low although citrate did enter the cells, was metabolized rapidly, did not interfere with the metabolism of ACh and the distribution of radioactivity from it in subcellular fractions of the brain was exactly the same as from [2-14C]pyruvate. It appears unlikely that citrate, glutamate or acetate act as transporters of intramitochondrially generated acetyl groups for the biosynthesis of ACh. Carnitine increased the incorporation of label from [1-14C]acetate into brain lipids and lowered its incorporation into ACh. Differences in the degree of labelling which various radioactive precursors produce in brain glutamine as compared to glutamate, previously described after intravenous, intra-arterial, or intraperitoneal administration, were confirmed using direct administration into the cerebrospinal fluid. Specific radioactivities of brain glutamine were higher than those of glutamate after injections of [1-14C]acetate, [2-14C]acetate, [1-14C]butyrate, [1,5-14C]citrate, [3H]acetylaspartate, [U-14C]leucine, and also after [2-14C]pyruvate and [4-14C]acetoacetate. The intracisternal route possibly favours the entry of substrates into the glutamine-synthesizing (‘small’) compartment. Increasing the amount of injected [2-14C]pyruvate lowered the glutamine/glutamate specific radioactivity ratio. The incorporation of 14C from [1-14C]acetate into brain lipids was several times higher than that from other compounds. By the extent of incorporation into brain lipids the substrates formed four groups: acetate > butyrate, acetoacetate, 3-hydroxybutyrate, citrate > pyruvate, lactate, acetylaspartate > glucose, glutamate. The ratios of specific radioactivity of ‘citrate’ over that of ACh and of glutamine over that of ACh were significantly higher after the administration of [1-14C]acetate than after [2-14C]pyruvate. The results indicate that the [1-14C]acetyl-CoA arising from [1-14C]acetate does not enter the same pool as the [1-14C]acetyl-CoA arising from [2-14C]pyruvate, and that the cholinergic nerve endings do not form a part of the acetate-utilizing and glutamine-synthesizing (‘small’) metabolic compartment in the brain. The distribution of radioactivity in subcellular fractions of the brain after the injection of [1-14C]acetate was different from that after [1, 5-14C]citrate. This suggests that [1-14C]acetate and [1, 5-14C]citrate are utilized in different subdivisions of the ‘;small’ compartment. 相似文献
18.
Ronald M. Sans Walter W. Jolly Robert A. Harris 《Archives of biochemistry and biophysics》1980,200(2):336-345
In the absence of any other oxidizable substrate, the perfused rat heart oxidizes [1-14C]leucine to 14CO2 at a rapid rate and releases only small amounts of α-[1-14C]ketoisocaproate into the perfusion medium. The branched-chain α-keto acid dehydrogenase complex, assayed in extracts of mitochondria prepared from such perfused hearts, is very active. Under such perfusion conditions, dichloroacetate has almost no effect on [1-14C]leucine oxidation, α-[1-14C]ketoisocaproate release, or branched-chain α-keto acid dehydrogenase activity. Perfusion of the heart with some other oxidizable substrate, e.g., glucose, pyruvate, ketone bodies, or palmitate, results in an inhibition of [1-14C]leucine oxidation to 14CO2 and the release of large amounts of α-[1-14C]ketoisocaproate into the perfusion medium. The branched-chain α-keto acid dehydrogenase complex, assayed in extracts of mitochondria prepared from such hearts, is almost completely inactivated. The enzyme can be reactivated, however, by incubating the mitochondria at 30 °C without an oxidizable substrate. With hearts perfused with glucose or ketone bodies, dichloroacetate greatly increases [1-14C]leucine oxidation, decreases α-[1-14C]ketoisocaproate release into the perfusion medium, and activates the branched-chain α-keto acid dehydrogenase complex. Pyruvate may block dichloroacetate uptake because dichloroacetate neither stimulates [1-14C]leucine oxidation nor activates the branched-chain α-keto acid dehydrogenase complex of pyruvate-perfused hearts. It is suggested that leucine oxidation by heart is regulated by the activity of the branched-chain α-keto acid dehydrogenase complex which is subject to interconversion between active and inactive forms. Oxidizable substrates establish conditions which inactivate the enzyme. Dichloroacetate, known to activate the pyruvate dehydrogenase complex by inhibition of pyruvate dehydrogenase kinase, causes activation of the branched-chain α-keto acid dehydrogenase complex, suggesting the existence of a kinase for this complex. 相似文献
19.
—Acetyl-CoA:choline-O-acetyltransferase (ChAc, EC 2.3.1.6) was purified from rat cerebral cortex and its half-life determined. The molecular weight of the enzyme under non-denaturing conditions was estimated by gel filtration to be in the range of 60,000–65,000. On SDS acrylamide gels, the purified enzyme migrated as a single band with a molecular weight estimated as 62,000. The turnover rate of ChAc in the mature rat was determined by the double label method, employing l -[1-14C]leucine and l -[4,5-3H]leucine. Its half-life under steady-state conditions was estimated to be 5.2 days. As a control, tubulin was isolated from the same preparation and its half-life measured. Under these conditions tubulin exhibited a half-life of 3.8 days. 相似文献
20.
Brain cortex slices from fed, 48 h and 120 h fasted rats were incubated and 14CO2 was measured from (a) [U-14C]glucose (5 mm ) either alone or in the presence of l -lcucine (0.1 or 1 mm ), and (b) [U-14C]leucine or [l-14C]leucine at 0.1 or 1 mm with or without glucose (5 mm ). In other experiments, sodium dl -3-hydroxybutyrate (3-OHB) or acetoacetate (AcAc) at 1 or 5 mm were added in the above incubation mixture. The rate of conversion of [U14C]glucose to CO2 was decreased 20% by leucine at 1 mm and 30–50% by 3-OHB at 1 or 5 mm but not by leucine at 0.1 mm . The effects of 3-OHB and of leucine (1 mm ) were not additive. The effects of leucine were similar in the fed and fasted rats. The rate of conversion of [U-14C]leucine or [l-,4C]leucine to 14CO2 at 0.1 mm and 1.0 mm was increased by glucose (35%) in the fed or fasted rats. Ketone bodies in the absence of glucose had no effect on leucine oxidation. However, the stimulatory effect of glucose on the rate of conversion of leucine to CO2 was inhibited by 3-OHB at 5 mm . These results suggest that (a) leucine in increased concentrations (1 mm ) may reduce glucose oxidation by brain cortex while itself becoming an oxidative fuel for brain, and (b) leucine oxidation by brain may be influenced by the prevailing glucose and ketone concentrations. 相似文献