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.