标题:Enzymatic identification of mannose 6-phosphate on the recognition marker for receptor-mediated pinocytosis of beta-glucuronidase by human fibroblasts
期刊名称:Proceedings of the National Academy of Sciences
印刷版ISSN:0027-8424
电子版ISSN:1091-6490
出版年度:1979
卷号:76
期号:9
页码:4322-4326
DOI:10.1073/pnas.76.9.4322
语种:English
出版社:The National Academy of Sciences of the United States of America
摘要:Human beta-glucuronidase (beta-D-glucuronide glucuronosohydrolase, EC 3.2.1.31 ), like many other glycoprotein lysosomal hydrolases, is subject to receptor-mediated endocytosis by fibroblasts. Prior work demonstrated charge heterogeneity in beta-glucuronidase and showed that high-uptake forms are more acidic than slowly internalized forms. Considerable indirect evidence implicated mannose 6-phosphate as an essential part of the recognition marker on high-uptake enzyme forms. Here we report the purification of beta-glucuronidase from human spleen and demonstrate enzymatically that mannose 6-phosphate is released on acid hydrolysis of pure 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. Thus, these studies provide direct evidence that mannose 6-phosphate is present on high-uptake enzyme forms, that it is present in the recognition marker for uptake, and that it is present on oligosaccharide that is released by endoglycosidase H.