Effect of dietary branched-chain alpha-keto acids on hepatic branched-chain alpha-keto acid dehydrogenase in the rat
Khatra, B.S.; Chawla, R.K.; Wadsworth, A.D.; Rudman, D.
Journal of Nutrition 107(8): 1528-1536
1977
ISSN/ISBN: 0022-3166 PMID: 886392 Document Number: 121827
Male albino rats (80-100 g) were tube-fed for 3 days with a complete purified amino acid diet minus valine, or this diet containing 70-210 .mu.mol/g of valine (1-3 times the minimal daily requirement, MDR) or equimolar amounts of its .alpha.-keto analogue (KIV [.alpha.-ketoisovaleric acid]); complete diet minus leucine, or this diet containing 85-225 .mu.mol/g of either leucine (1-3 times the MDR) or its .alpha.-keto analogue (KIC [.alpha.-ketoisocaproic acid]); complete diet minus valine, leucine and isoleucine, or this diet containing 63-170 .mu.mol/g of these amino acids (1-2 times the MDR) or their .alpha.-keto analogues (KIV, KIC, KMV [.alpha.-keto-.beta.-methylvaleric acid]). Liver and kidney were then assayed for dehydrogenase activity towards substrates KIV, KIC, KMV, pyruvate and .alpha.-ketoglutarate. Both the branched-chain amino acids (BCAA) and their .alpha.-keto analogues (BCKA) stimulated the activity of branched-chain hepatic dehydrogenases. BCKA were 2-9 times more potent than BCAA in this respect. The effect was specific for enzyme and organ, since dehydrogenase activity for .alpha.-ketoglutarate and pyruvate in liver, and dehydrogenase activity for BCKA, pyruvate and .alpha.-ketoglutarate in kidney, were not increased. Dietary BCKA (1-2 times MDR) accelerated the decarboxylation of KIC by slices of liver 2-6 times without altering the rate of transamination to leucine. Decarboxylation of KIC by kidney and muscle slices was unaffected. The stimulation of hepatic branched-chain dehydrogenase by BCKA may play a role in the limited nutritional efficiency of these N-free substitutes for the BCAA compared to .alpha.-keto analogues of other essential amino acids.