Inhibition of coenzyme activation of aspartate aminotransferase

Forty compounds were surveyed for their effect on the activation of pig heart apoaspartate aminotransferase by pyridoxamine 5'-phosphate. Most of the nucleotides, sugar phosphates, coenzymes, phospholipid precursors and inorganic oxyanions tested were found to be inhibitory. With few exceptions, the only requirement for a substance to be inhibitory is the presence of a di- or polyanionic moiety analogous to the 5'-phosphate group of the cofactor. In spite of the lack of overall structural similarity to pyridoxamine 5'-phosphate, inorganic pyrophospate and apparently other inhibitors are characterized by dissociation constants comparable in magnitude to that previously reported for the natural cofactor. The physiological significance of the inhibition of coenzyme activation of apoaspartate aminotransferase by these common biological compounds is not known.