New tetrazolium method for the histochemical demonstration of gamma-glutamyl transpeptidase

A new tetrazolium method for the histochemical demonstration of gamma-gluta myl transpeptidase is proposed. The method is based on a newly synthesized substrate-gamma-l-glutamic acid-1-hydroxy-4-naphthylamide, which upon the e nzyme hydrolysis liberates 1,4-aminonaphthol-a powerful reducing agent that reduces tetrazolium salts quickly and quantitatively to deeply colored, wa ter-insoluble formazans, precipitating on the sites of the enzyme activity and marking them accurately. The redox reaction is quick enough and does no t need any auxiliary electron-acceptor. The method is very fast and conveni ent for the histochemical visualization of the enzyme.