Regulation of branched chain amino acid metabolism in ruminants.

The regulation of branched-chain amino acid (BCAA) metabolism has been studied in ruminants mainly during the last decade. Evidences support that the rate of BCAA catabolism is lower in ruminants than in monogastrics. This is associated with a low specific BCAA aminotransferase (first catabolic enzyme) activity and a relatively low degree of activation of the second catabolic enzyme in post-natal ruminant tissues. Similarly to monogastrics in vivo BCAA catabolism involves an interorgan cooperation in ruminants. The benefic effect of leucine excess in protein turnover has also been raised. By contrast leucine excess does not stimulate the rate of isoleucine and valine catabolism in ruminants as much as in monogastrics.