KINETICS OF BRAIN GLUTAMATE DECARBOXYLASE. INHIBITION STUDIES WITH N‐(5′‐PHOSPHOPYRIDOXYL) AMINO ACIDS 1

Abstract— Seven N‐(5′‐phosphopyridoxyl) amino acids, reduced analogs of the glutamate‐pyridoxal phosphate Schiff base, were synthesized and purified. All of them inhibited mouse brain glutamate decarboxylase activity. The four most potent inhibitors were the aminooxyacetate, GABA, cysteinesul‐finate and glutamate derivatives, and the effect of these compounds was studied kinetically. The inhibition produced was in all cases mixed function with respect to glutamate and competitive with respect to pyridoxal phosphate. The inhibition kinetics were non‐linear. These results are interpreted in terms of an ordered binding of pyridoxal phosphate and glutamate to the enzyme. Furthermore, they are consistent with previous findings suggesting the existence of two kinds of glutamate decarboxylase activity differing in their dependence on free pyridoxal phosphate.