Physiological covalent regulation of rat liver branched-chain α-ketoacid dehydrogenase
A radiochemical assay was developed for measuring branched-chain α-ketoacid dehydrogenase activity of Triton X-100 extracts of freeze-clamped rat liver. The proportion of active (dephosphorylated) enzyme was determined by measuring enzyme activities before and after activation of the complex with a...
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Published in | Archives of biochemistry and biophysics Vol. 243; no. 2; pp. 542 - 555 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
San Diego, CA
Elsevier Inc
01.12.1985
Elsevier |
Subjects | |
Online Access | Get full text |
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Summary: | A radiochemical assay was developed for measuring branched-chain α-ketoacid dehydrogenase activity of Triton X-100 extracts of freeze-clamped rat liver. The proportion of active (dephosphorylated) enzyme was determined by measuring enzyme activities before and after activation of the complex with a broad-specificity phosphoprotein phosphatase. Hepatic branched-chain α-ketoacid dehydrogenase activity in normal male Wistar rats was 97% active but decreased to 33% active after 2 days on low-protein (8%) diet and to 13% active after 4 days on the same diet. Restricting protein intake of lean and obese female Zucker rats also caused inactivation of hepatic branched-chain α-ketoacid dehydrogenase complex. Essentially all of the enzyme was in the active state in rats maintained for 14 days on either 30 or 50% protein diets. This was also the case for rats maintained on a commercial chow diet (minimum 23% protein). However, maintaining rats on 20, 8, and 0% protein diets decreased the percentage of the active form of the enzyme to 58, 10, and 7% of the total, respectively. Fasting of chow-fed rats for 48 h had no effect on the activity state of hepatic branched-chain α-ketoacid dehydrogenase, i.e., 93% of the enzyme remained in the active state compared to 97% for chow-fed rats. However, hepatic enzyme of rats maintained on 8% protein diet was 10% active before starvation and 83% active after 2 days of starvation. Thus, dietary protein deficiency results in inactivation of hepatic branched-chain α-ketoacid dehydrogenase complex, presumably as a consequence of low hepatic levels of branched-chain α-ketoacids, established inhibitors of branched-chain α-ketoacid dehydrogenase kinase. With rats fed a low-protein diet and subsequently starved, inhibition of branched-chain α-ketoacid dehydrogenase kinase by branched-chain α-ketoacids generated as a consequence of endogenous proteolysis most likely promotes the greater branched-chain α-ketoacid dehydrogenase activity state. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0003-9861 1096-0384 |
DOI: | 10.1016/0003-9861(85)90531-4 |