Aminotransferase Activity of α-Aminoisobutyric Acid Decomposing Enzyme

Abstract

The enzyme which decomposes α-aminoisobutyric acid (AIB) to acetone in presence of pyruvate is active to various α-dialkyl-α-amino acids. From relative rates of decomposition of AIB, L-(+)isovaline, 2-ethyl-2-aminobutyrate and D-(-)isovaline, it was suggested that a carbon chain having a configuration of natural D-amino acids was required for the enzyme action.
On the other hand, this enzyme catalyzes the transamination between L-alanine and α-ketobutyrate. The equilibrium constant in the direction of L-α-aminobutyrate formation is 0.62. Electrophoretic migration, α-keto acid specificity and pH dependence of the aminotransferase activity were similar to those of AIB decomposing activity. Moreover, both activities increased in cells incubated by either L-α-aminobutyrate or AIB.