This review covers recent results on the ability of pyridoxal phosphate, either alone or as an enzyme cofactor of enzymes, to catalyze reactions with amino acids. Although pyridoxal phosphate catalyzes many different reactions in water solutions, its reaction specificity is quite poor. In biological systems, both reaction and substrate specificity is determined by apoenzymes. So far, more than twenty structures of pyridoxal 5´-phosphate-dependent enzymes have been solved. Most of them are evolutionarily related to aspartate aminotransferase. On the basis of structure motifs, they have been divided into four families with aspartate aminotransferase, tryptophan synthase, D-amino acid transferase and alanine racemase as representatives. A remarkable convergent evolution is observed in two fold types with a similar cofactor binding and reaction mechanism.