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

ABSTRACT: 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.

SUBMITTER: Zhao Y

PROVIDER: S-EPMC1132286 | biostudies-other | 1993 Mar

REPOSITORIES: biostudies-other

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Project description:Rates of transamination and decarboxylation of [1-14C]leucine at a physiological concentration (0.1 mM) were measured in the perfused rat heart. In hearts from fasted rats, metabolic flux through the branched-chain 2-oxo acid dehydrogenase reaction was low initially, but increased gradually during the perfusion period. The increase in 14CO2 production was accompanied by an increase in the amount of active branched-chain 2-oxo acid dehydrogenase complex present in the tissue. In hearts from rats fed ad libitum, extractable branched-chain dehydrogenase activity was low initially, but increased rapidly during perfusion, and high rates of decarboxylation were attained within the first 10 min. Infusion of glucagon, adrenaline, isoprenaline, or adrenaline in the presence of phentolamine all produced rapid, transient, inhibition (40-50%) of the formation of 4-methyl-2-oxo[1-14C]pentanoate and 14CO2 within 1-2 min, but the specific radioactivity of 4-methyl-2-oxo[14C]pentanoate released into the perfusate remained constant. Glucagon and adrenaline infusion also resulted in transient decreases (16-24%) in the amount of active branched-chain 2-oxo acid dehydrogenase. In hearts from fasted animals, infusion for 10 min of adrenaline, phenylephrine, or adrenaline in the presence of propranolol, but not infusion of glucagon or isoprenaline, stimulated the rate of 14CO2 production 3-fold, and increased 2-fold the extractable branched-chain 2-oxo acid dehydrogenase activity. These results demonstrate that stimulation of glucagon or beta-adrenergic receptors in the perfused rat heart causes a transient inhibition of branched-chain amino acid metabolism, whereas alpha-adrenergic stimulation causes a slower, more sustained, enhancement of branched-chain amino acid metabolism. Both effects reflect interconversion of the branched-chain 2-oxo acid dehydrogenase complex between active and inactive forms. Also, these studies suggest that the concentration of branched-chain 2-oxo acid available for decarboxylation can be regulated by adrenaline and glucagon.

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

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