A sensitive automated colorimetric method for the determination of serum gamma-glutamyl transpeptidase

A highly sensitive and accurate automated method using a Technicon Autoanalyzer AAII was developed for the determination of human serum gamma-glutamyl transpeptidase. gamma-L-Glutamyl-p-nitroanilide added as substrate was split to p-nitroaniline and the gamma-glutamyl group was trapped by glycylglycine in Ammediol/HC1 buffer solution. Liberated p-nitroaniline was diazotized and converted by Tsuda Reagent (N,N-(diethyl)-N'-(1-naphthyl) ethylendiamine) to an azo-dye possessing an absorbance maximum at 550 nm. This new method of determination, using the conversion of p-nitroaniline to azo-dye, was found to be 7 times more sensitive as compared to the conventional direct p-nitroaniline determination method [1]. This method requires only 0.1 ml lerum and permits 60 determinations per hour.