Comparison of coenzymatic activities of 2-nor-2-hydroxymethyl pyridoxal 5′-phosphate for mitochondrial and cytoplasmic aspartate aminotransferases

2-Nor-2-hydroxymethyl pyridoxal 5′-phosphate served as a somewhat superior coenzyme to pyridoxal 5′-phosphate for cytoplasmic and mitochondrial aspartate aminotransferases in the usual assay system containing Tris-HCl buffer. In the presence of phosphate anion, however, the affinities of the analog for both enzymes and the V values of the reactions mediated by the cytoplasmic and mitochondrial aspartate aminotransferases reconstituted with the analog were more markedly decreased than in the cases of the native coenzyme. Various Vitamin B₆ enzymes tested hitherto were classified into at least three groups according to their attitudes toward the coenzyme analog.