Studies on the intestinal disaccharidases of the pigeon II. Subcellular localization and solubilization

In the pigeon, 70-80% of the activities of maltase (αD-glucoside glucohydrolase EC 3.2.1.20), sucrase (αglucohydrolase, EC 3.2.1.48), isomaltase (dextran 6-αD-glucan hydrolase, EC 3.2.1.10) and glucoamylase (1,4-αD-glucan glucohydrolase, EC 3.2.1.3) were found to be localized in the brush-border membrane of intestinal epithelial cells. Of the total glycosidase activities in the mucosal homogenate, nearly 60 to 70% were recovered in the microsomal (105 000 × g) fraction, about 30% in the mitochondrial (22 000 × g) fraction and less than 5% from the cytosol (105 000 x g supernatant) fraction. The hydrolases were solubilized by digestion with papain but not with trypsin, and the phosphate ion had a protective effect in the solubilization. Amongst detergents, Triton X-100 but not sodium deoxycholate, was found to truly solubilize these enzymes.