A new assay method of γ-glutamyltransferase with 4-aminobenzoate hydroxylase from Agaricus bisporus as a coupling enzyme

We have developed a new ultraviolet spectrophotometric method for measurement of serum gamma-glutamyltransferase activity. The principle of the method is as follows. Using L-gamma-glutamyl-3-chloro-4-aminobenzoate as the donor substrate, 3-chloro-4-aminobenzoate formed upon transfer of the gamma-glutamyl moiety from the donor substrate to the acceptor substrate glycylglycine is stoichiometrically converted to 3-chloro-4-hydroxyaniline by 4-aminobenzoate hydroxylase from Agaricus bisporus, coupled with the oxidation of NADH to NAD+, and the resulting decrease in absorbance at 340 nm is monitored. The results obtained indicate that there is a good possibility to establish an ultraviolet spectrophotometric method for measurement of serum gamma-glutamyltransferase activity using L-gamma-glutamyl-3-chloro-4-aminobenzoate as the donor substrate and 4-aminobenzoate hydroxylase from Agaricus bisporus as a coupling enzyme.