Interaction of Pyridoxamine-pyruvate Transaminase with Carbonyl Derivatives of Pyridoxal.

on pyridoxine or pyridoxamine as a sole source of carbon and nitrogen (1, 2). This transaminase contains no pyridoxal phosphate, and hence provides a simpler system for mechanistic studies than do the more complex, pyridoxal phosphate-containing transaminases. The enzyme binds pyridoxamine and pyridoxal with almost equal avidity; the latter is bound in part by an azomethine Iinkage to the e-amino group of a lysine residue of the enzyme (2). During the determination of the specificity of this enzyme, a relatively slow formation of pyridoxamine was noted when pyridoxal oxime or certain other carbonyl derivatives of pyridoxal were substituted for pyridoxal as substrate in Reaction 1. Further studies, described herein, reveal that these substances do not undergo transamination directly, but instead interact with the enzyme to form enzyme-bound pyridoxal, which then undergoes transamination. The results are of interest in connection with claims (3-7) that various derivatives of pyridoxal-P, e.g. the hydrazone, oxime, isonicotinoylhydrazone, act per se as coenzymes for certain pyridoxal phosphate-dependent enzymes.