Physiological covalent regulation of rat liver branched-chain α-ketoacid dehydrogenase

Robert Harris, Steven M. Powell, Ralph Paxton, Sarah E. Gillim, Hidetoshi Nagae

Research output: Contribution to journalArticle

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Abstract

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.

Original languageEnglish
Pages (from-to)542-555
Number of pages14
JournalArchives of Biochemistry and Biophysics
Volume243
Issue number2
DOIs
StatePublished - 1985

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3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)
Liver
Rats
Nutrition
Diet
Enzymes
Protein-Restricted Diet
Proteins
Starvation
Phosphotransferases
Zucker Rats
Protein Deficiency
Dietary Proteins
Phosphoprotein Phosphatases
Proteolysis
Octoxynol
Enzyme activity
Wistar Rats
Fasting
Assays

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology

Cite this

Physiological covalent regulation of rat liver branched-chain α-ketoacid dehydrogenase. / Harris, Robert; Powell, Steven M.; Paxton, Ralph; Gillim, Sarah E.; Nagae, Hidetoshi.

In: Archives of Biochemistry and Biophysics, Vol. 243, No. 2, 1985, p. 542-555.

Research output: Contribution to journalArticle

Harris, Robert ; Powell, Steven M. ; Paxton, Ralph ; Gillim, Sarah E. ; Nagae, Hidetoshi. / Physiological covalent regulation of rat liver branched-chain α-ketoacid dehydrogenase. In: Archives of Biochemistry and Biophysics. 1985 ; Vol. 243, No. 2. pp. 542-555.
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