scholarly journals Effects of clofibric acid on the activity and activity state of the hepatic branched-chain 2-oxo acid dehydrogenase complex

1992 ◽  
Vol 285 (1) ◽  
pp. 167-172 ◽  
Author(s):  
Y Zhao ◽  
J Jaskiewicz ◽  
R A Harris
Keyword(s):  
Active Form ◽  
Clofibric Acid ◽  
Chow Diet ◽  
Acid Dehydrogenase ◽  
Low Protein ◽  
Activity State ◽  
Branched Chain ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

Feeding clofibric acid to rats caused little or no change in total activity of the liver branched-chain 2-oxo acid dehydrogenase complex (BCODC). No change in mass of liver BCODC was detected by immunoblot analysis in response to dietary clofibric acid. No changes in abundance of mRNAs for the BCODC E1 alpha, E1 beta and E2 subunits were detected by Northern-blot analysis. Likewise, dietary clofibric acid had no effect on the activity state of liver BCODC (percentage of enzyme in the dephosphorylated, active, form) of rats fed on a chow diet. However, dietary clofibric acid greatly increased the activity state of liver BCODC of rats fed on a diet deficient in protein. No stable change in liver BCODC kinase activity was found in response to clofibric acid in either chow-fed or low-protein-fed rats. Clofibric acid had a biphasic effect on flux through BCODC in hepatocytes prepared from low-protein-fed rats. Stimulation of BCODC flux at low concentrations was due to clofibric acid inhibition of BCODC kinase, which in turn allowed activation of BCODC by BCODC phosphatase. Inhibition of BCODC flux at high concentrations was due to direct inhibition of BCODC by clofibric acid. The results suggest that the effects of clofibric acid in vivo on branched-chain amino acid metabolism can be explained by the inhibitory effects of this drug on BCODC kinase.

scholarly journals Regulation of the branched-chain 2-oxo acid dehydrogenase complex in hepatocytes isolated from rats fed on a low-protein diet

1986 ◽  
Vol 234 (2) ◽  
pp. 285-294 ◽  
Author(s):  
R A Harris ◽  
R Paxton ◽  
G W Goodwin ◽  
S M Powell
Keyword(s):  
Protein Diet ◽  
Low Protein Diet ◽  
Chow Diet ◽  
Acid Dehydrogenase ◽  
Low Protein ◽  
Activity Measurements ◽  
Activity State ◽  
Branched Chain ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

Hepatocytes isolated from rats fed on a chow diet or a low-protein (8%) diet were used to study the effects of various factors on flux through the branched-chain 2-oxo acid dehydrogenase complex. The activity of this complex was also determined in cell-free extracts of the hepatocytes. Hepatocytes isolated from chow-fed rats had greater flux rates (decarboxylation rates of 3-methyl-2-oxobutanoate and 4-methyl-2-oxopentanoate) than did hepatocytes isolated from rats fed on the low-protein diet. Oxidizable substrates tended to inhibit flux through the branched-chain 2-oxo acid dehydrogenase, but inhibition was greater with hepatocytes isolated from rats fed on the low-protein diet. 2-Chloro-4-methylpentanoate (inhibitor of branched-chain 2-oxo acid dehydrogenase kinase), dichloroacetate (inhibitor of both pyruvate dehydrogenase kinase and branched-chain 2-oxo acid dehydrogenase kinase) and dibutyryl cyclic AMP (inhibitor of glycolysis) were effective stimulators of branched-chain oxo acid decarboxylation with hepatocytes from rats fed on a low-protein diet, but had little effect with hepatocytes from rats fed on chow diet. Activity measurements indicated that the branched-chain 2-oxo acid dehydrogenase complex was mainly (96%) in the active (dephosphorylated) state in hepatocytes from chow-fed rats, but only partially (50%) in the active state in hepatocytes from rats fed on a low-protein diet. Oxidizable substrates markedly decreased the activity state of the enzyme in hepatocytes from rats fed on a low-protein diet, but had much less effect in hepatocytes from chow-fed rats. 2-Chloro-4-methylpentanoate and dichloroacetate increased the activity state of the enzyme in hepatocytes from rats fed on a low-protein diet, but had no effect on the activity state of the enzyme in hepatocytes from chow-fed rats. The results indicate that protein starvation greatly increases the sensitivity of the hepatic branched-chain 2-oxo acid dehydrogenase complex to regulation by covalent modification.

scholarly journals Role of activation of myocardial branched-chain 2-oxo acid dehydrogenase complex in the regulation of leucine decarboxylation during cardiac work in vitro

1987 ◽  
Vol 248 (2) ◽  
pp. 423-428
Author(s):  
E Hildebrandt ◽  
M S Olson
Keyword(s):  
Flow Rate ◽  
Coronary Flow ◽  
Active Form ◽  
Oxidative Decarboxylation ◽  
Cardiac Work ◽  
Acid Dehydrogenase ◽  
Branched Chain ◽  
Langendorff Hearts ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

The oxidative decarboxylation of L-[1-14C]leucine was measured in the isolated perfused rat heart under both working and non-working conditions. Stimulation of decarboxylation of the labelled substrate was observed in working hearts as cardiac work was increased, and in Langendorff hearts upon increasing the coronary flow rate. The rate of L-[1-14C]leucine decarboxylation was significantly higher (P less than 0.05) in hearts working against moderate afterload pressure when compared to Langendorff hearts perfused at a matching coronary flow rate. The rate of release of 4-methyl-2-oxo[1-14C]pentanoate to the perfusate was high in Langendorff hearts, and was unaffected by changes in coronary flow. In contrast, perfusate levels of 14C-labelled 4-methyl-2-oxopentanoate decreased significantly upon the establishment of the working condition (P less than 0.05). These findings suggested an enhancement in the efficiency of the decarboxylation of the 2-oxo acid in response to cardiac work. The amount of branched-chain 2-oxo acid dehydrogenase complex present in the active form was measured in freeze-clamped hearts. Cardiac work resulted in a rapid activation of the complex (P less than 0.02) within 5 min of work when compared to control Langendorff hearts perfused at matching coronary flow rates. To a lesser extent, increasing the coronary flow rate in Langendorff-perfused hearts also led to activation of the enzyme complex. These studies suggest the following: a) L-leucine oxidation in myocardial tissue can be accelerated by exercise as it is in other tissues; b) this regulatory response can be evoked by the contractile activity of the heart itself, independent of contributions by circulating factors or nervous stimuli; and c) regulation of the activity state of the branched-chain 2-oxo acid dehydrogenase complex is involved in the mechanism by which metabolic flux through this pathway is controlled during cardiac work.

Nutritional and Hormonal Regulation of the Activity State of Hepatic Branched-Chain ?-Keto Acid Dehydrogenase Complex

1989 ◽  
Vol 573 (1 Alpha-Keto Ac) ◽  
pp. 306-313 ◽  
Author(s):  
ROBERT A. HARRIS ◽  
GARY W. GOODWIN ◽  
RALPH PAXTON ◽  
PAUL DEXTER ◽  
STEVEN M. POWELL ◽  
...  
Keyword(s):  
Hormonal Regulation ◽  
Keto Acid ◽  
Acid Dehydrogenase ◽  
Activity State ◽  
Branched Chain ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

scholarly journals Quantitative control analysis of branched-chain 2-oxo acid dehydrogenase complex activity by feedback inhibition

1990 ◽  
Vol 271 (2) ◽  
pp. 523-528 ◽  
Author(s):  
B Boyer ◽  
R Odessey
Keyword(s):  
Feedback Inhibition ◽  
Regulatory Control ◽  
Control Factor ◽  
Control Analysis ◽  
Complex Activity ◽  
Acid Dehydrogenase ◽  
Branched Chain ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

The potential for branched-chain 2-oxo acid dehydrogenase complex (BCOADC) activity to be controlled by feedback inhibition was investigated by calculating the Elasticity Coefficients for several feedback inhibitors. We suggest that feedback inhibition is a quantitatively important regulatory mechanism by which branched-chain 2-oxo acid dehydrogenase activity is regulated. The potential for control of enzyme activity is greater for NADH than for the acyl-CoA products, and suggests that factors that alter the redox potential may physiologically regulate BCOADC activity through a feedback inhibitory mechanism in vivo. Local pH may also be an important regulatory control factor.

scholarly journals Effect of starvation and exercise on actual and total activity of the branched-chain 2-oxo acid dehydrogenase complex in rat tissues

1984 ◽  
Vol 223 (3) ◽  
pp. 815-821 ◽  
Author(s):  
A J M Wagenmakers ◽  
J T G Schepens ◽  
J H Veerkamp
Keyword(s):  
Skeletal Muscle ◽  
Total Activity ◽  
Treadmill Running ◽  
Whole Body ◽  
Acid Dehydrogenase ◽  
Liver And Kidney ◽  
Activity State ◽  
Branched Chain ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

Starvation does not change the actual activity per g of tissue of the branched-chain 2-oxo acid dehydrogenase in skeletal muscles, but affects the total activity to a different extent, depending on the muscle type. The activity state (proportion of the enzyme present in the active state) does not change in diaphragm and decreases in quadriceps muscle. Liver and kidney show an increase of both activities, without a change of the activity state. In heart and brain no changes were observed. Related to organ wet weights, the actual activity present in the whole-body muscle mass decreases on starvation, whereas the activities present in liver and kidney do not change, or increase slightly. Exercise (treadmill-running) of untrained rats for 15 and 60 min causes a small increase of the actual activity and the activity state of the branched-chain 2-oxo acid dehydrogenase complex in heart and skeletal muscle. Exercise for 1 h, furthermore, increased the actual and the total activity in liver and kidney, without a change of the activity state. In brain no changes were observed. The actual activity per g of tissue in skeletal muscle was less than 2% of that in liver and kidney, both before and after exercise and starvation. Our data indicate that the degradation of branched-chain 2-oxo acids predominantly occurs in liver and to a smaller extent in kidney and skeletal muscle in fed, starved and exercised rats.

scholarly journals Developmental pattern of branched-chain 2-oxo acid dehydrogenase complex in rat liver and heart

1993 ◽  
Vol 290 (2) ◽  
pp. 395-399 ◽  
Author(s):  
Y Zhao ◽  
S C Denne ◽  
R A Harris
Keyword(s):  
Developmental Pattern ◽  
Neonatal Rat ◽  
Milk Formula ◽  
Mrna Levels ◽  
Suckling Period ◽  
Acid Dehydrogenase ◽  
Branched Chain ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

The developmental pattern of the branched-chain 2-oxo acid dehydrogenase complex was examined in the liver and heart of the rat throughout the suckling period. Basal activity and total activity of the complex were measured as a function of age. The hepatic enzyme activity increased dramatically and was 100% active (dephosphorylated) during the suckling period. The level of protein kinase associated with the complex was particularly low at birth, but like the complex increased throughout the suckling period. The level of heart enzyme also increased as a function of age, but only about 30-45% of the enzyme was active throughout the suckling period. Very low protein levels of liver and heart branched-chain 2-oxo acid dehydrogenase were detected by immunoblot analysis in newborn rats. The mRNA levels for the liver E1 alpha, E1 beta, and E2 subunits in newborn rat were 30%, 19%, and 4% of adult levels respectively. The capacity of the neonatal rat for oxidizing leucine in vivo was low at birth and increased with age. 4-Methyl-2-oxopentanoate was more toxic when given to newborn and 3-day-old pups than 21-day-old pups, as expected from the relative capacities of their tissues to dispose of branched-chain 2-oxo acids by oxidation. Force-feeding suckling rats a protein-free artificial milk formula resulted in partial inactivation of the hepatic branched-chain 2-oxo acid dehydrogenase complex, indicating that the liver of the suckling rat can adapt to conserve branched-chain amino acid residues during periods of protein deficiency.

scholarly journals Activity of branched-chain 2-oxo acid dehydrogenase complex in rat liver mitochondria and in rat liver

1988 ◽  
Vol 256 (3) ◽  
pp. 929-934 ◽  
Author(s):  
M Beggs ◽  
P J Randle
Keyword(s):  
Rat Liver ◽  
Specific Activity ◽  
Active Form ◽  
Rat Liver Mitochondria ◽  
Acid Dehydrogenase ◽  
Liver Concentration ◽  
Branched Chain ◽  
Protein Free Diet ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

Four mitochondrial marker enzymes were used to show that: (1) high-protein (24%) diet increased the rat liver concentration and content of total branched-chain 2-oxo acid dehydrogenase complex (BCDC) by 31% by increasing mitochondrial specific activity of BCDC; (2) starvation increased the liver concentration of BCDC by 25% by decreasing liver weight; the liver content of mitochondria and the mitochondrial specific activity of BCDC were unchanged; (3) protein-free diet decreased rat liver BCDC concentration and content by 20%, by decreasing the liver concentration and content of mitochondria. Protein-free diet increased liver mitochondrial specific activities of L-glutamate, 2-oxoglutarate and NAD-isocitrate dehydrogenases. The validity of a mitochondrial method for the determination of the liver concentration of BCDC and the percentage in the active form in vivo is confirmed, and improvements are described. The experimental basis of criticisms of its use in this regard by Zhang, Paxton, Goodwin, Shimomura & Harris [(1987) Biochem. J. 246, 625-631] was not confirmed. The finding by Harris, Powell, Paxton, Gillim & Nagae [(1985) Arch. Biochem. Biophys. 243, 542-555], that starvation has no effect on the percentage of BCDC in the active form in rat liver, is confirmed.

Activation of branched-chain alpha-keto acid dehydrogenase complex by exercise: effect of high-fat diet intake

1990 ◽  
Vol 68 (1) ◽  
pp. 161-165 ◽  
Author(s):  
Y. Shimomura ◽  
T. Suzuki ◽  
S. Saitoh ◽  
Y. Tasaki ◽  
R. A. Harris ◽  
...  
Keyword(s):  
Amino Acids ◽  
Branched Chain Amino Acids ◽  
Enzyme Complex ◽  
Keto Acid ◽  
High Fat ◽  
Acid Dehydrogenase ◽  
Activity State ◽  
Branched Chain ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

The effect of exercise on the activity of branched-chain alpha-keto acid dehydrogenase complex in liver and muscle was studied in rats fed a high-fat (FAT) or a high-carbohydrate (CHO) diet. Both diet groups of rats were offered isoenergetic diets by a meal-feeding method and were trained by treadmill running. On the final day of the experiment, half of the rats in each diet group were exercised by 2 h of running just before they were killed. The activity state of the enzyme complex was elevated maximally by exercise in liver of rats fed the FAT diet but not in liver of rats fed the CHO diet, suggesting that catabolism of branched-chain amino acids in rat liver during exercise was enhanced by the FAT diet. The activity state of the enzyme complex in muscle was enhanced by exercise in both groups of rats, but a significant difference was not observed between the groups. The concentration of branched-chain amino acids was elevated in liver and muscle by exercise in both groups of rats, but the elevated levels in liver were lower in rats fed the FAT diet than in those fed the CHO diet. Serum branched-chain amino acid concentrations were significantly lower in rested rats fed the FAT diet than in those fed the CHO diet, and the leucine and isoleucine concentrations in the former were elevated by exercise, but the serum concentrations in the latter were not significantly affected by exercise. ATP and ADP concentrations in muscle were not significantly affected by either diet or exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Effects of diet and of alloxan-diabetes on the activity of branched-chain 2-oxo acid dehydrogenase complex and of activator protein in rat tissues

1984 ◽  
Vol 222 (3) ◽  
pp. 711-719 ◽  
Author(s):  
P A Patston ◽  
J Espinal ◽  
P J Randle
Keyword(s):  
Alloxan Diabetes ◽  
Active Form ◽  
Standard Diet ◽  
Activator Protein ◽  
Low Protein ◽  
Liver And Kidney ◽  
Branched Chain ◽  
Protein Diets ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

The total activities (sum of active and inactive forms) of branched-chain 2-oxo acid dehydrogenase complex in tissues of normal rats fed on a standard diet were (unit/g wet wt.): liver, 0.82; kidney, 0.77; heart, 0.57; hindlimb skeletal muscles, 0.034. Total activity was decreased in liver by 9%- or 0%-casein diets and by 48 h starvation, but not by alloxan-diabetes. Total activities were unchanged in kidney and heart. The amount of active form of the complex (in unit/g wet wt. and as % of total) in tissues of normal rats fed on standard diet was: liver, 0.45, 55%; kidney, 0.55, 71%; heart, 0.03, 5%; skeletal muscle less than 0.007, less than 20% (below lower limit of assay). The concentration of the active form of the complex was decreased in liver and kidney, but not in heart, by low-protein diets, 48 h starvation and alloxan-diabetes. In heart muscle alloxan-diabetes increased the concentration of active complex. The concentration of activator protein (which activates phosphorylated complex without dephosphorylation) in liver and kidney was decreased by 70-90% by low-protein diets and 48 h starvation. Alloxan-diabetes decreased activator protein in liver, but not in kidney. Evidence is given that in tissues of rats fed on a normal diet approx. 70% of whole-body active branched chain complex is in the liver and that the major change in activity occasioned by low-protein diets is also in the liver.

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