Gamma-glutamyltransferase: evaluation of a new method.

The determination of gamma-glutamyltransferase using a new donor substrate, L-gamma-glutamyl-3,5-dibromo-4-hydroxyanilide, was evaluated in two laboratories. Between-run and within-run precision are excellent and comparable with those of other methods for the determination of gamma-glutamyltransferase. The activity concentrations of gamma-glutamyltransferase from human sera obtained with the new donor substrate were slightly higher than those obtained with L-gamma-glutamyl-4-nitroanilide. The reverse was found for sera enriched with gamma-glutamyltransferase of animal origin. Temperature conversion factors (activity 37 degrees C/activity 30 degrees C) are given. The advantages of this method are discussed. The new assay appears to provide a good alternative for the method with L-gamma-glutamyl-4-nitroanilide or one of its derivatives as substrate.