New tetrazolium method for the histochemical localization of dipeptidyl peptidase IV

New tetrazolium method for the histochemical localization of dipeptidyl pep tidase IV (DPP TV), based on a newly synthesized substrate Gly-L-Pro-1-hydr oxy-4-naphthylamide is proposed. Upon the enzyme hydrolysis of the substrat e a strong reducing agent, i.e. 4-amino-1-naphthol is released, which reduc es tetrazolium salts to water-insoluble, deeply colored formazans, that pre cipitate on the sites of enzyme activity, marking them accurately. No auxil iary electron acceptor is needed for the redox reaction. The incubation is performed at the optimal pH of the enzyme. Precise enzyme localization is a chieved in all organs studied. Thus, the new method avoids most of the disa dvantages of the methods in use and might open new possibilities in peptida ses histochemistry.