The effects of maltitol on rat intestinal disaccharidases.

1. The highese disaccharidase activity for sucrose maltose and maltitol was found in the jejunum, followed by the ileum and duodenum. However, the disaccharidase activity for maltitol was extremely low compared with that for sucrose and maltose. 2. For maltitol, the Km value was very large and the Vmax value was very low compared compared with the values for sucrose and maltose. 3. The initial velocity (v) in the presence of the sucrose and maltitol, was equal to the sum of the rates for individual substrates sucrose ann maltitol (v1, v2) respectively (v=v1+v2). Thus, no competition between these substrates was observed. In the case of maltose and maltitol, the initial velocity (v) in the presence of both substrates was less than the sum of the individual rates for maltose and maltitol (v1, v2) in the absence of the other substrate (v is less than v1 + v2). This finding demonstrates that there is competition between these two substrates for the same enzyme. Furthermore, the apparent Michaelis constant (Km) and the apparent maximal velocity (Vmax) for pure and mixed substrates, i.e., maltose and maltitol, at various mole fractions of maltose showed dependence on the mole fraction of maltose. The obtained kinetic data provide strong evidence that both maltose and maltitol react at the single active center of maltase.