Gamma-glutamyltransferase (γ-GT) catalyzes the transfer of a γ- glutamyl group from γ-glutamyl-3-carboxy-4-nitroanilide to glycylglycine with the formation of L-γ-glutamyl-glycylglycine and 5 amino-2-nitro-benzoate.
The amount of 5-amino-2-nitro-benzoate formed, monitored kinetically at 405 nm, is proportional to the enzyme activity present in the sample.