Degradation of branched-chain amino acids and their derived 2-oxo acids and fatty acids in human and rat heart and skeletal muscle

Abstract

Studies were made on the oxidation of the branched-chain amino acids, leucine and valine, and their derived 2-oxo acids and branched-chain short-chain fatty acids in intact muscular preparations and homogenates of man and rat. In rat hemidiaphragm transamination rates of the amino acids are higher than oxidative decarboxylation rates and oxidative decarboxylation rates of the 2-oxo acids are higher than those of the corresponding amino acids at the same concentration. The last phenomenon also was observed in rat- and human-heart slices. Transaminase and 2-oxo acid dehydrogenase activities are much higher in homogenates than in intact preparations from the same muscle. Homogenates from heart muscle have generally a higher transaminase and 2-oxo acid dehydrogenase activity than those from skeletal muscle and those from rat muscle have higher activities than those from comparable human muscle. Homogenates from rat heart and liver have similar 2-oxo acid dehydrogenase activities. In homogenates and mitochondria, CO 2 was only produced by oxidative decarboxylation of the branched-chain 2-oxo acids and no CO 2 was produced from the corresponding branched-chain short-chain fatty acids. In all intact muscular preparations the branched-chain 2-oxo acids were oxidized more to completeness and CO 2 production from the coresponding short-chain fatty acids was observed. The further degradation of the branched-chain 2-oxo acids beyond α-decarboxylation appeared to be limited, for 3-methyl-2-oxobutanoate still more than for 4-methyl-2-oxopentanoate.