Feeding rats a high fat/carbohydrate ratio diet reduces jejunal S/I activity ratio and unsialylated galactose on glycosylated chain of S-I complex.

Aims: We examined whether decreasing jejunal sucrase/isomaltase (S/I) activity ratio by feeding rats a high fat/carbohydrate ratio diet is regulated by changing glycosylated chains on the S-I complex.

Main Methods: Jejunal activities of sucrase, isomaltase and beta-1,4-galactosyltransferase were examined in rats fed a high fat/carbohydrate or a low fat/carbohydrate ratio diet. The amount of galactose and mannose in the glycosylated chain on the S-I complex in rats fed both diets was determined using RCA(120) and Con A lectins, respectively. The effects of reducing unsialylated galactose from the glycosylated chain on the S-I complex were assessed by determining sucrase activity in purified S-I complex treated with beta-galactosidase.

Key Findings And Significance: Feeding rats a high fat/carbohydrate ratio diet reduced jejunal S/I activity ratio in mucosal homogenates and purified fractions. The level of unsialylated galactose in glycosylated chains on the S-I complex was reduced by feeding rats a high fat/carbohydrate ratio diet. The form with reduced levels of unsialylated galactose had lower sucrase activity than that with more unsialylated galactose. The reduction of galactose on the S-I complex by beta-galactosidase in vitro reduced sucrase activity. Feeding rats a high fat/carbohydrate ratio diet also reduced jejunal beta-1,4-galactosyltransferase activity. Taken together, decreasing the S/I activity ratio by feeding rats a high fat/carbohydrate diet is associated with the reduction of unsialylated galactose on the glycosylated chain of the S-I complex.