Changes of γ-Glutamyltransferase Gene Expression of Livers in Weanling Rats Fed a Low Soybean Protein Isolate Diet

Abstract

The effect of a low soybean protein isolate (SPI) diet on hepatic γ-glutamyltransferase (γGT) activity was studied in weanling rats. Weanling Wistar rats fed a 10% SPI diet, which has a low tnethionine content (about 50% that of a 10% casein diet, 1.4g/kg diet), showed about a five-fold increase in hepatic γGT activity at 3 weeks, compared with that of rats maintained on a 10% casein diet. This increase was suppressed by addition of methionine to the SPI diet, but not altered by addition of cystine. Thus, the elevation of γGT activity in the liver of rats fed the SPI diet might be attributable to insufficiency of methionine in the diet. The increase of γGT was explainable by changes in γGT-speeific mRNA, as revealed by Northern blot and dot-blot hybridization analyses, since the γGT mRNA level increased to almost the same extent as the level of activity. These results suggest that the increase of γGT activity induced by the SPI diet Was brought abaut by an increase in the amount of γGT mRNA.