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A colorimetric assay for γ-glutamyl transpeptidase (γ-GTP; E.C 2.3.2.2) employing 2,4,6-trinitrobenzene sulfonate (TNBS) to detect the amount of disappeared acceptor via transpeptidation, has been developed. Under the experimental conditions using L-γ-glutamyl ethylester and L-phenylalanine as γ-glutamyl donor and acceptor, respectively, it was found that the decreased absorbance of yellow color at 420 nm was strictly related to the amount of L-γ-glutamyl-L-phenylalanine (L-γ-Clu-L-Phe) formed, which was determined by DEAE-cellulose column chromatography. Concentrations of the enzyme and γ-glutamyl products were able to be determined in the nanogram and nanomoles per milliliter range, respectively, with high precision and reliability. This novel assay system may therefore be a useful means for understanding of catalytic function of the γ-GTP spectrophotcmetrically without any usage of sophisticated instruments.
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