Reagent and process for the determination of the activity of the enzyme gamma-glutamyl transferase

The present invention provides a process for the kinetic determination of gamma -glutamyl transferase activity by the reaction of a gamma -glutamylarylamide with the formation of an arylamine at a pH value of from 6 to 10, wherein the arylamine is simultaneously reacted with an aromatic amine or phenol appropriate as a coupling component and an appropriate oxidation agent to give a colored compound with an absorption maximum above 565 nm, the rate of formation of which is monitored photometrically and is used as a measure for the gamma -glutamyl transferase activity. The present invention also provides a reagent for the kinetic determination of gamma -GT activity, wherein it contains the following reagents: gamma -GT-arylamide:1-100 mmol/l. gamma -glutamyl acceptor (glycylglycine):10-500 mmol/l. coupling component:1-500 mmol/l. oxidation agent:0.1-500 mmol/l. buffer:10-1000 mmol/l.