A new chromogenic substrate for angiotensin-converting enzyme

The compound para-nitrobenzyloxycarbonylglycyl-(S-4-nitrobenzo-2-oxa- 1,3-diazole)-L-cysteinylglycine [NO2ZGly(S-NBD)CysGly] with an absorption maximum at 423 nm is readily hydrolyzed by angiotensin-converting enzyme (EC 3.4.15.1. peptidlyldipeptide hydrolase) to yield the S-benzfurazan derivative of cysteinylglycine. An internal S-->N shift occurs immediately to yield the N-benzfurazan derivative which in turn reacts with the sulfhydryl reagent 4,4'-dithiodipyridine to produce the mixed disulfide with an intense absorption at 461 nm. The maximum difference in molar absorptivity of 13,000 M-1 cm-1 occurs at 470 nm.