New approach to the metabolism of hydrogenated starch hydrolysate: hydrolysis by the maltase/glucoamylase complex of the rat intestinal mucosa.

The maltase (EC 3.2.1.20)/glucoamylase (EC 3.2.1.3) complex from rat small intestine brush border, which is able to split alpha (1----4) glucose-sorbitol linkage, was isolated and purified by chromatography on DEAE-Trisacryl M and Sepharose 6B. The complex was homogeneous on polyacrylamide gel electrophoresis. Kinetic parameters were studied on two substrates: maltose and maltitol (Km:1.3 mM and 30 mM, Vmax:200 nmol X min-1 and 15 nmol X min-1, respectively). Inhibition studies were performed with maltose and maltitol as substrates and isomaltitol and delta-gluconolactone as inhibitors. Crossed-inhibition reactions were also performed. The results support the existence of one single catalytic site and this fact was confirmed by physicochemical properties. Similar results were obtained with germ-free rats as well as with conventional rats adapted over 6-12 months to Lycasin 80/55 as the sole source of sugar. Lycasin 80/55, hydrogenated starch hydrolysate, was converted by purified maltase/glucoamylase complex in glucose and sorbitol.