STUDIES ON THE DISTRIBUTION AND KINETICS OF THE ALKALINE PHOSPHATASE OF RAT SMALL INTESTINE

Abstract

Alkaline phosphatase activity was demonstrated throughout the entire length of the small intestine of the albino rat and the relative amounts present seemed to decrease exponentially from the pylorus to the ileocolic valve. All subcellular fractions of intestinal homogenates were found to hydrolyze sodium β-glycero-phosphate. The distribution of activity of the enzyme was as follows: "microsomes", about 76%; nuclei, 10%; mitochondria, 8%; and in the nongranular, supernatant fraction, 9%. The specific activity for these fractions was: 52, 3, 10, and 3, respectively. The effects of the time of incubation, pH of the hydrolytic mixture, and the concentration of the enzyme were similar in all fractions. For the enzyme in the various fractions slight differences were observed in the values of the Michaelis constants, and in the degree of activation by magnesium ion. These variations may be explained on the basis of differences in the accessibility of substrate and magnesium ion to the enzymes in the various fractions. The finding that the "microsomes" contained the highest levels of alkaline phosphatase suggests that this intestinal enzyme is produced almost entirely by these submicroscopic particles.