THE HISTOCHEMICAL DEMONSTRATION OF ENZYMATIC ACTIVITY BY A NONENZYMATIC REDOX REACTION. REDUCTION OF TETRAZOLIUM SALTS BY INDOLYL-3-ACETALDEHYDE

Abstract

The availability of synthetic indolyl-3-acetaldehyde has made possible the determination of the mechanism of reduction of tetrazolium salts in the tryptamine-tetrazolium technique for the demonstration of monoamine oxidase activity. This aldehyde, formed as the result of the enzymatically catalyzed oxidative deamination of tryptamine, directly reduces sensitive tetrazolium salts to localize monoamine oxidase activity in tissue sections. No implication of a diaphorase-like system in the reduction of the tetrazoles was found. The possibility of a pigment precursor being formed as the result of the oxidation of the indolyl aldehyde during tetrazole reduction is discussed and the utilization of a similar scheme of nonenzymatic reduction of an indicator dye for demonstrating both oxidative and hydroytic enzyme systems is presented.