Gamma glutamyl transpeptidase: measurement and development in guinea pig small intestine.

Abstract

A modification ofa previous method for the assay ofy glutamyI transpeptidase (GGTP) was developed. Substrate solubility difficulties alluded to by other investigators were avoided by employing heating and solubilization of the chromogenic substrate y glutamyl-P-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 ofhigh 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.