Hydrolysis of Glucosyl-sucrose and Maltosyl-sucrose in Rat Intestinal Brush Border Membrane

Abstract

Hydrolysis of glucosy-sucrose (G₂F) and maltosyl-sucrose (G₃F) were studied in the brush border of rat intestinal mucosa and compared with those of sucrose and maltose.
Maximum hydrolyzing activities of G₂F and G₃F were reached at the substrate concentration of 6mM. Optimum pH was 6.0. Hydrolyzing activities of G₂F and G₃F by intestinal brush border were comparable to that of maltose.
The intial velocity of hydrolysis in the presence of G₂F or G₃F was less than the sum of the individual rates for G₂F and sucrose or G₃F and sucrose. This result suggests that there is competition between these two substrates for the same enzyme. Furthermore, the apparent Michaelis constant (K_m) and the apparent maximum velocity (V_max) for pure and mixed substrates, i. e. G₂F and sucrose or G₃F and sucrose, at various mole fractions (f) of G₂F or G₃F showed dependence on the mole fraction of G₂F or G₃F, and provided strong evidence that this competitive inhibition reacts at the same active center of sucrase. Furthermore, the similar results were observed in maltose and G₂F or G₃F.