RAT INTESTINAL SUCRASE: I. INTESTINAL DISTRIBUTION AND REACTION KINETICS

Abstract

A study of the distribution of sucrase (invertase) activity in the small intestine of the rat and of sucrase reaction kinetics was conducted. Sucrase activity was measured in water homogenates of 10-cm sections of the intestine. The sucrase activity of normal adult male rats was associated mainly with the first half of the small intestine (measured from the pylorus) and decreased to negligible amounts at the ileocolic end. A trace of sucrase activity was found in the colon, but other rat tissues examined lacked the enzyme.The third 10-cm section of the small intestine (measured from the pylorus) was used as a source of enzyme for studies of reaction kinetics. The optimum pH for intestinal sucrase was 6.25 under the conditions used. The optimum substrate concentration was 0.12 M (4.1%) to 0.5 M (17.1%) sucrose, and the K_m was 0.0128 M. At the sucrose concentration used for routine assays (0.161 M) the enzyme action was zero order for a period of at least 20 minutes. Sucrase action followed the Arrhenius equation at temperatures between 5° and 37 °C, and an activation energy of 10,100 calories per mole was calculated.