Distribution of branched-chain alpha-keto acid dehydrogenases in primate tissues

The specific activity of the branched-chain alpha-keto acid (BCKA) dehydrogenases was measured in normal tissues of the rat, monkey, and man, and in cirrhotic human liver. In the rat, specific activity of the dehydrogenases in liver, kidney, and muscle averaged 33, 26, and 0.4 U/g wet tissue, respectively; proportion of the body's content of the enzyme located in these three organs was 70, 12, and 10%. In the monkey, specific activities in liver and kidney were only one-half to one-third as great as in the rat, whereas activity in muscle was the same; the monkey's body content of dehydrogenase was distributed 50% in liver, 13% in kidney, and 20% in muscle. In man, specific activities in liver and kidney were only 1/15th to 1/25th as great as in the rat, but activity in skeletal muscle was the same. Distribution of the dehydrogenases in man was 30% in liver, 2% in kidneys, and 60% in muscle. In six patients with alcoholic cirrhosis, specific activity of the dehydrogenase in liver was reduced to 20-50% of normal (average, 32%). This reduction may alter the efficiency of BCKA as substitutes for branched-chain amino acids when BCKA are administered orally, but will have little influence on efficiency when they are given intravenously.