Characterization of Microbial ω-Amino Acid Transaminases and The Bound Coenzymes

Abstract

ω-Amino acid transaminases catalyze the transamination of ω-amino acids with pyruvate and α-ketoglutarate as an amino donor. The distribution of the transaminases in microorganisms has been described with the emphasis on those of ω-amino acid: pyruvate transaminase (ω-APT) and γ-aminobutyrate transaminase (GABA-T). The GABA-T activity has been demonstrated in various microorganisms, though ω-APT was found in bacteria and yeasts. The reactivity of GABA-T toward β-alanine was related to the presence of ω-APT in the microorganisms. The enzymologic properties of the purified and crystallized transaminases have been described. These transaminases were inhibited by carbonyl reagents and SH reagents except ω-APT. The enzymes have been also characterized for spectral properties, coenzyme contents, suicide substrate reaction and stereochemistry of the reaction. Protein chemical studies revealed no homology between ω-amino acid transaminases and other PLP enzymes. Three dimensional structure of ω-APT has been determined at 2.0 A resolution and showed high degree of homology between ω-APT and aspartate transaminase in the supersecondary structure around active site region.