ò-Leucine (beta-leucine) is a beta amino acid and positional isomer of -leucine which is naturally produced in humans via the metabolism of -leucine by the enzyme leucine 2,3-aminomutase. In cobalamin (vitamin B<sub>12</sub>) deficient individuals, plasma concentrations of ò-leucine are elevated.
A small fraction of metabolism â less than 5% in all tissues except the testes where it accounts for about 33% â is initially catalyzed by leucine aminomutase, producing ò-leucine, which is subsequently metabolized into (ò-KIC), ò-ketoisocaproyl-CoA, and then acetyl-CoA by a series of uncharacterized enzymes.