Transamination reactions in Saccharomyces fragilis.

Abstract

Summary: A dialysed cell-free extract of Saccharomyces fragilis Jörgensen was found to catalyse the transfer of the amino group from alanine, aspartic acid, isoleucine, leucine, norleucine, methionine, ornithine, phenylalanine, tryptophan, tyrosine or valine to α-ketoglutaric acid with the production of glutamic acid and the corresponding keto acid. The transaminase reactions leading to the formation of alanine, aspartic acid, phenylalanine or tryptophan from glutamic acid and the corresponding keto acid were also catalysed by the yeast extract. The addition of pyridoxal phosphate to the incubation mixture increased the rate of transamination between α-ketoglutaric acid and any one of the following amino donors: aspartic acid, leucine, methionine, phenylalanine, tryptophan or tyrosine. The rate of formation of glutamic acid from α-ketoglutaric acid and leucine was most rapid at pH 8, but the rate of amino transfer from aspartic acid did not vary with pH over the range 6·0–9·0. The equilibrium constant for the aspartic-glutamic transamination reaction was found to be 2·2 at pH 7·8 and 37 °. The transfer of the amino group from aspartic acid or leucine to α-ketoglutaric acid was not inhibited by any one of five antibiotics tested, but was partially inhibited by 10−3 m-semicarbazide.