ExtractA modification of a previous method for the assay of γ glutamyl transpeptidase (GGTP) was developed. Substrate solubility difficulties alluded to by other investigators were avoided by employing heating and solubilization of the chromogenic substrate γ glutamyl-β-naphthylamide in a medium of carbonate 0.05 M and Tris buffer 0.1 M at pH 9.5. The kinetics and conditions for such an assay are described. Whole intestinal homogenates of adult male guinea pigs were used as the source of the enzyme.The developmental pattern of this enzyme was determined in fetuses at 55 and 63 days of gestation and at varying times from 1 to 90 days of age. A total of 69 animals was assayed. The general pattern was that of high specific activity during prenatal life, with a rapid decline during the neonatal period (3–24 days of age) and a slight increase after 55 days of age.Other guinea pig organs were studied. Liver and kidney were found to contain enzyme activity greater than that of the intestine. Subcellular fractionation of intestinal mucosa using ultracentrifugation revealed a twenty-fold enrichment of activity in jejunal brush border membrane, compared with whole jejunal homogenates when expressed as specific enzyme activity per mg of protein. The stability characteristics of GGTP disclosed no loss of specific activity when stored at −28° for 50 days.This simple enzyme assay, stability of the enzyme when frozen, subcellular distribution in the intestinal brush border membrane, and an unusual developmental pattern made this enzyme a useful adjunct to the study of intestinal protein metabolism.SpeculationThe unique ability of GGTP to hydrolyze > glutamic acid-peptide bonds and the location of the enzyme in the intestinal brush border suggest a role for this enzyme in the metabolism of an unusual group of physiologically important peptides such as glutathione, folic acid, and gluten-gliadin. The significance of these γ-bonded compounds may now be approached in order to investigate the role of this enzyme in gluten enteropathy and related disorders.