Leucine Metabolism of Streptococcus Lactis VAR. Maltigenes. II. Transaminase and Decarboxylase Activity of Acetone Powders

Abstract

Acetone powders of both S. lactis and S. lactis var. maltigenes possess a transaminase system which effects the transfer of the amino group of leucine to alpha-ketoglutaric acid resulting in the formation of alpha-ketoisocaproic acid and glutamic acid. This enzyme system is believed to require pyridoxal phosphate as a cofactor and is active at pH 8.4. Although the cell preparations effected the removal of the amino group from leucine at pH 4.6, no conversion of alpha-keto-glutaric acid to glutamic acid was observed. Manometric studies demonstrated the presence of a thiamine pyrophosphate mediated alpha-ketoisocaproic acid decarboxylase in dialyzed acetone powders of S. lactis var. maltigenes which was absent in similar preparations of S. lactis. Detection of 3-methyl-butanal in the reaction mixtures from manometric studies confirmed the decarboxylative mechanism.