New method for the histochemical demonstration of dipeptidyl aminopeptidase I activity using a novel anthraquinoyl hydrazide substrate

A new method for the histochemical localization of dipeptidyl aminopeptidas e I (DPP I, cathepsin C), based on a newly synthesized substrate-Gly-L-Phe- 5-chloro-1-anthraquinoyl hydrazide.HCl (Gly-Phe-CAH), is proposed. The enzy me activity liberates 5-chloro-1-anthraquinoyl hydrazine (CAH) - a water-in soluble brown-reddish compound, which precipitates on the enzyme locations. The primary reaction product reacts simultaneously or, otherwise, by post- coupling with p-anisaldehyde (p-AA), thus converting to the reddish-violet amorphous hydrazone - the final reaction product. The validity of enzyme lo calization is thus assured by the insolubility of the primary reaction prod uct and does not depend on the rate of the second reaction step. The enzyme studied is successfully localized in different rat organs using the newly proposed technique.