A colorimetric assay for γ-glutamyltranspeptidase

A highly sensitive and simple colorimetric method for the assay of γ-glutamyltranspeptidase is described. As substrate, l-γ- glutamyl-p- nitroanilide has been used, which is dissolved with glycylglycine and MgCl 2 in ammediol—HCl buffer. The enzyme splits the substrate in the γ-glutamyl group and p-nitroaniline, the γ-glutamyl group is bound by the glycylglycine. The p-nitroaniline, which has a maximum absorbance at 405 ± 10 nm, is used as an indicator to detect the enzyme activity. The reaction is stopped by adding 0.0075 N NaOH. The end colour is stable, the incubation time 45 min and only 2 × 0.1 ml serum is needed; if stored at 4°, the enzyme activity is stable for more than two weeks. The first results are promising and γ-glutamyltranspeptidase seems to be a useful additional routine liver function test.