Demonstration of sucrase-isomaltase complex in chick intestine.

It was investigated whether sucrase and isomaltase form an enzyme-enzyme complex in chick intestine or not, and some properties of the disaccharidases were compared with those of other species. 1) Chick intestinal sucrase and isomaltase were shown to exist in the form of an enzyme-enzyme complex from the results of polyacrylamide disc gel electrophoresis, DEAE Sephadex A-25 ion exchange column chromatography and citraconylation, although the chick intestinal sucrase and isomaltase were not retained on a Sephadex G-200 column. 2) The molecular weights of sucrase-isomaltase complex, maltase I, maltase II, maltase III and isomaltase dissociated from sucrase-isomaltase complex were estimated to be 250,000, 250,000, 160,000, 225,000 and 80,000, respectively, by polyacrylamide disc gel electrophoresis. 3) The optimum pH for all the enzymes was 6.0. 4) Km values of sucrase, isomaltase, maltase I and maltase III were 10.0, 3.5, 1.0 and 4.6 mM, respectively. Vmax values for sucrase, isomaltase, maltase I and maltase III were 217.4, 281.4, 147.1 and 454.5 mumol substrate hydrolyzed/mg protein/hr, respectively.