Initial catabolic steps of isoleucine, the R-pathway and the origin of alloisoleucine

The initial catabolic steps of isoleucine by mammals has been misunderstood and misapprehended in the scientific literature for many years. The sugges tion that the interconversion of isoleucine and alloisoleucine occurs throu gh the keto-enol racemization of their respective transaminated alpha -keto acids was first tentatively advanced by Alton Meister in the early 1950s, and accepted without hard confirming evidence by many authors. It will be s hown in this brief review that isoleucine is converted to alloisoleucine wi th conservation of a N-15 label denying the intermediacy of the alpha -keto acids, and that alloisoleucine arises as an unavoidable consequence of iso leucine transamination. (C) 2001 Elsevier Science B.V. All rights reserved.