ENZYMATIC IDENTIFICATION OF MANNOSE 6-PHOSPHATE ON THE RECOGNITION MARKER FOR RECEPTOR-MEDIATED PINOCYTOSIS OF BETA-GLUCURONIDASE BY HUMAN-FIBROBLASTS

.beta.-Glucuronidase was purified from human spleen. It was demonstrated enzymatically that mannose 6-phosphate is released on acid hydrolysis of pure enzyme. The mannose 6-phosphate content of the enzyme varies directly with its susceptibility to pinocytosis by fibroblasts. Enzyme forms resolved by CM-Sephadex chromatography differed over an 18-fold range in uptake rate and in mannose 6-phosphate content. The most acidic forms had 4.4 mol of mannose 6-phosphate per mol of enzyme. The mannose 6-phosphate was released from the enzyme by treatment with endoglycosidase H with concomitant loss of susceptibility to adsorptive endocytosis. Mannose 6-phosphate is present on high-uptake enzyme forms; it is present in the recognition marker for uptake; it is present on oligosaccharide that is released by endoglycosidase H.