Pyridoxal enzymes: mechanistic diversity and uniformity.

Pyridoxal 5'-phosphate (PLP) acts as the coenzyme in a vast number of reactions in amino acid metabolism. The study of PLP enzymes is one of the most fascinating frontiers in enzymology, and now the mechanism s of several types of PLP enzymes are being discussed at the atomic level based on crystallographic, spectroscopic, and site-directed mutagenesis studies. In this review, I summarize the important findings, including those provided by classical studies, on the reaction mechanisms of several PLP enzymes, with the intention of discussing the chemically and thermodynamically consistent principle of the catalytic action of PLP enzymes common to all the enzymes of this group, and the uniqueness of individual enzymes that endows them substrate and reaction specificity.