Evidence for alpha-proton abstraction and carbanion formation involving a functional histidine residue in lentil seedling amine oxidase.

Lentil seedling amine oxidase catalyzes the oxidation of putrescine and in the presence of tetranitromethane gives rise to the formation of nitroform anion. The initial rate of substrate and enzyme-dependent nitroform production is linearly related to the functional active site content and is proportional to the tetranitromethane concentration. Diethylpyrocarbonate modifies two histidyl residues on the lentil amine oxidase. Incubation of the enzyme with diethylpyrocarbonate at 25 degrees C and pH 7.0 irreversibly inhibits enzyme activity by a pseudo first-order kinetics process. The data obtained are consistent with the enzyme-dependent abstraction of an alpha-proton from the substrate to form an intermediate enzyme bound carbanion and indicate a functional role for histidine in lentil amine oxidase catalysis consistent with that of a general base in proton abstraction.