The hydrolysis of sucrose by intact and homogenized cells of rat small intestine. Influence of pH and substrate concentration

The intracellular locus of sucrose hydrolysis in rat small-intestinal mucosa has been studied in vitro using intestinal slices and homogenates of intestinal cells. The pH-activity curves for the invertase of the slices and homogenates were identical. The apparent K_m for the invertase activity of the slices was considerably higher than the K_m for the homogenates. The maximum velocity (V) for the slices and homogenates was nearly identical. Because of the difference in the apparent K_m values, it is postulated that a barrier exists between the apical surface of the cell and the site of hydrolysis of sucrose by invertase. Since the barrier slows the transport of sucrose to the enzyme in the intact cells but permits rapid pH equilibration between the enzyme locus and the fluid bathing and brush border, the barrier may be located superficially.