Properties of human intestinal glucoamylase

1. 1. Human intestinal glucoamylase has been purified almost to homogeneity by polyacrylamide disc electrophoresis. At least two isoenzymes were found with identical catalytic properties. 2. 2. Linear oligosaccharides (N = 9) containing glucose residues linked α(1 → 4) have the greatest affinity for the active site. Both decreasing and increasing the polysaccharide chain length increased the K_m. 3. 3. The purified enzyme hydrolyzed both α(1 → 4) linkages and α(1 → 6) linkages. Linear glucose polymers linked α(1 → 4) were hydrolyzed more rapidly than polymers containing α(1 → 6) cross linkages. Activity of the purified enzyme against both linkages was identically heat inactivated, and no sucrase activity was detectable. Thus, hydrolysis of α(1 → 6) bands was not due to contamination by intestinal sucrase-isomaltase. 4. 4. Intestinal glucoamylase contained 32-38% carbohydrate by weight, and had a partial specific volume of 0.684. 5. 5. Molecular weight of the purified enzyme was 210 000 by equilibrium sedimentation. 6. 6. The purified enzyme contained neither sialic acid nor phosphate, both membrane components. It is not clear yet whether a portion of glycocalyx might be removed with the enzyme during purification to account for the high carbohydrate content.