scholarly journals Effects of low-protein diet and starvation on the activity of branched-chain 2-oxo acid dehydrogenase kinase in rat liver and heart

1986 ◽  
Vol 237 (1) ◽  
pp. 285-288 ◽  
Author(s):  
J Espinal ◽  
M Beggs ◽  
H Patel ◽  
P J Randle
Keyword(s):  
Rat Liver ◽  
Kinase Activity ◽  
Liver Mitochondria ◽  
Normal Diet ◽  
Heart Mitochondria ◽  
Casein Diet ◽  
Acid Dehydrogenase ◽  
Low Protein ◽  
Branched Chain ◽  
Dehydrogenase Complex

The activity of branched-chain 2-oxo acid dehydrogenase kinase was 3-fold greater in extracts of heart mitochondria than in extracts of liver mitochondria from rats fed on normal diet. Feeding rats on a 0%-casein diet for 10 days increased the activity of branched-chain kinase 4-fold in extracts of liver mitochondria and in branched-chain dehydrogenase complex purified from such extracts; starvation (48 h) was without effect. In extract of heart mitochondria, kinase activity was increased 2-fold by feeding on 0%-casein diet and 1.5-fold by 48 h of starvation.

scholarly journals Rat tissue concentrations of branched-chain 2-oxo acid dehydrogenase complex. Re-evaluation by immunoassay and bioassay

1986 ◽  
Vol 235 (2) ◽  
pp. 429-434 ◽  
Author(s):  
P A Patston ◽  
J Espinal ◽  
J M Shaw ◽  
P J Randle
Keyword(s):  
Rat Liver ◽  
Chain Complex ◽  
Liver Mitochondria ◽  
Spectrophotometric Assay ◽  
Normal Diet ◽  
Casein Diet ◽  
Active Complex ◽  
Acid Dehydrogenase ◽  
Branched Chain ◽  
Acid Dehydrogenase Complex

A rabbit polyclonal antibody to purified ox kidney branched-chain oxo acid dehydrogenase complex was shown by a variety of techniques to be an antibody to the E2 (acyltransferase) component. Rocket immunoelectrophoresis showed that the antibody does not discriminate between phosphorylated (inactive) or dephosphorylated (active) complex, and the same technique is used to assay total branched-chain complex (sum of active and inactive forms) in rat liver and heart mitochondrial extracts. The values obtained in normal rats fed on normal diet were comparable with those obtained by spectrophotometric assay of the holocomplex reaction after conversion of inactive complex into active complex. The values obtained in liver mitochondria from rats fed on 0%-casein diet or starved for 48 h were comparable with those in rats fed on normal diet, whereas earlier studies using spectrophotometric assay had shown substantial decreases in rats fed on 0%-casein diet or starved for 48 h. It has been shown that conversion of inactive complex into active complex requires prolonged incubation (120 min) in the presence of ketoleucine (4-methyl-2-oxopentanoate; to inhibit branched-chain oxo acid dehydrogenase kinase) to effect complete conversion in mitochondria from rats fed on 0%-casein diet, or starved for 48 h, or made diabetic with alloxan. By this technique, total activity of the complex in rat liver mitochondria was unaffected by diet or diabetes. The effects of diet and diabetes to decrease the activity of branched-chain complex in rat liver are therefore apparently mediated wholly through inactivation of the complex by phosphorylation.

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 Purification of rat kidney branched-chain oxo acid dehydrogenase complex with endogenous kinase activity

1982 ◽  
Vol 204 (1) ◽  
pp. 353-356 ◽  
Author(s):  
R Odessey
Keyword(s):  
Pyruvate Dehydrogenase ◽  
Time Course ◽  
Kinase Activity ◽  
Rat Kidney ◽  
Pyruvate Dehydrogenase Complex ◽  
Acid Dehydrogenase ◽  
Endogenous Protein ◽  
Branched Chain ◽  
Acid Dehydrogenase Complex ◽  
Dehydrogenase Complex

A method was devised to purify branched-chain oxo acid dehydrogenase (BCOAD) from rat kidney which retains endogenous kinase activity. Incorporation of 32P into purified enzyme parallels the time course of enzyme inhibition by ATP. Phosphorylation occurs on a serine residue(s) of the 46000-mol.wt. subunit of the enzyme complex. Endogenous phosphatase activity is not present after purification, and added pyruvate dehydrogenase phosphate phosphatase does not re-activate BCOAD or liberate 32P from previously labelled enzyme. These results demonstrate that BCOAD can be regulated by an endogenous protein kinase and that the phosphorylation-cycle enzymes regulating BCOAD appear to be distinct from those associated with pyruvate dehydrogenase complex.

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.

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