A. Ferjancicbiagini et al., IN-VITRO OXIDATIVE DECARBOXYLATION OF L-2-HYDROXY-4-METHYLTHIOBUTANOIC ACID BY L-2-HYDROXY ACID OXIDASE-A FROM CHICKEN LIVER, Biochimie, 77(4), 1995, pp. 249-255
The first step in the set of reactions responsible for the biological
utilization of L-2-hydroxy-4-methylthiobutanoic acid, the methionine h
ydroxy analogue, in protein synthesis was investigated in vitro using
pure L-2-hydroxy acid oxidase A from chicken liver. The reaction yield
ed no more than 20% of the corresponding alpha-keto acid, 2-keto-4-met
hylthiobutanoic acid, the well-known intermediate in methionine metabo
lism, and as much as 80% of the subsequent decarboxylation product, 3-
methylthiopropionate, suggesting that L-2-hydroxy-4-methylthiobutanoic
acid cannot be completely converted into methionine in vivo. It was t
herefore concluded that chicken liver L-2-hydroxy acid oxidase, a pero
xisomal enzyme requiring flavin mononucleotide as a coenzyme, also has
an oxidative decarboxylation activity in vitro, which was found to be
NADH-dependent. The mechanism possibly underlying the successive conv
ersion of the methionine hydroxy analogue into alpha-keto acid and 3-m
ethylthiopropionate by this NADH:flavin oxidoreductase-decarboxylase a
ctivity is described.