Abstract
Class I α-mannosidases are thought to exist exclusively as integral membrane proteins that play intracellulary an essential role in the N-glycan biosynthesis. Using [ 3H]Man 9GlcNAc 2 as a substrate, we were able to identify a soluble α-mannosidase in human serum that trims the substrate Man 9GlcNAc 2 to Man 5-8GlcNAc 2 with Man 6GlcNAc 2 being the major product. This serum mannosidase is Ca 2+-dependent, sensitive to 1-deoxymannojirimycin but insensitive to the class II inhibitor swainsonine and, hence, belongs to class I mannosidases. The enzymatic properties of the serum class I mannosidase are similar to that of the membrane bound class I mannosidases Golgi-mannosidase IA and IB and Man 9-mannosidase.
Published Version
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