Abstract
Extract: The enzymatic activity hydrolyzing γ-glutamyl-β-naphthylamide (γ-glutamyltranspeptidase, GGTP) was studied in the small intestine of human adults and fetuses. Surgical biopsies taken from the proximal jejunum approximately 10 cm from the ligament of Treitz served as the source of the enzyme for adult subjects. The entire small bowel was obtained from fetuses of different ages and divided into three thirds for enzymatic assay. All samples were frozen immediately and used within 1–4 months. It was shown that enzymatic activities stored at −20° are stable for that period.
The GGTP activity was enhanced by the presence of glycylglycine in the incubation mixture, the maximal activation being 5.2-fold ± 0.65-fold (mean ± 1 sd) when the dipeptide concentration was 40 mM. The pH optimum for GGTP activity was 9.0 both in the presence and in the absence of glycylglycine. Glycylglycine activation and pH activity curves were similar for the proximal jejunum of adults and of two fetuses (17 and 20 weeks old).
The specific activity of GGTP significantly increased from the proximal to the distal third at every fetal age (P = 0.01–0.001). The specific GGTP activity (U/g protein) of the proximal jejunum of the adult was 2.2 ± 0.5 (mean ± 1 sd). It was thus approximately one-eighth that found in the proximal third of the fetal small bowel (18.4 ± 7.7 U/g protein).
In order to investigate the subcellular localization of GGTP activity, isolated brush borders and brush border membranes were prepared from surgical biopsies of adult proximal jejunum. The GGTP- and sucrase (EC. 3.2.1.26)-specific activities increased in a parallel way from the brush border to the membrane fraction. This result indicates that at least part of the GGTP activity is located in this membrane.
Speculation: The physiologic significance of GGTP activity in the intestine is still conjectural. If it is involved in intestinal digestion, the high levels of the enzyme present in the fetus enable the neonate to digest γ-glutamyl peptides.
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Auricchio, S., Ciccimarra, F., Vegnente, A. et al. Enzymatic Activity Hydrolyzing γ-Glutamyl-β-Naphthylamide in Human Intestine during Adult and Fetal Life. Pediatr Res 7, 95–99 (1973). https://doi.org/10.1203/00006450-197302000-00005
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DOI: https://doi.org/10.1203/00006450-197302000-00005