Maleic Hydrazide and Isonicotinyl Hydrazide as Carbonyl Reagents

Abstract

Abstract The effects of maleic hydrazide (MH) and isonicotinyl hydrazide (INH) on the reactions catalyzed by pea cotyledon amine oxidase, carrot root l‐glutamic decarboxylase, and wheat seedling transaminase have been studied. The activity of amine oxidase is inhibited if it is incubated with MH or INH before the addition of substrate, and it is also dependent on the time of preincubation. The effect of MH and INH is depressed or prevented by α‐ketoglutarate, pyruvate, pyridoxal phosphate, and pyridoxal but not pyridoxine, reduced glutathione, cysteine, or CuCl2. MH and INH inhibit the l‐aspartate transamination by wheat mitochondria. They only slightly inhibit the decarboxylation of l‐glutamate by the carrot root enzyme. The role of MH and INH is discussed as carbonyl reagents in plant metabolism. decarboxylase. Thus, the mechanism by which Mh and INH inhibit action of l‐glutamic decarboxylase is rather complicated and will not be elucidated very soon. The inhibition of aspartate transamination by MH and INH can be interpreted in terms of two processes: the combination of the inhibitors with α‐ketogultarate and pyridoxal phosphate which is a coenzyme of the transaminase. Since transamination is one of the most important reactions in the amino acid metabolism controlling the protein level in living cells, the effect of MH and INH should be noticed as shown above. Kim and Greulach (1963) report that MH and 5‐fluorouracil markedly reduce the content of free amino acids and DNA in Chlorella pyrenoideas; this in interesting in view of the present results concerning the transamination.