Characterization of a soluble class I alpha-mannosidase in human serum. |
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| Authors: | S Porwoll H Fuchs R Tauber |
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| Institution: | Institut für Laboratoriumsmedizin und Pathobiochemie, Medizinische Fakult?t Charité der Humboldt-Universit?t zu Berlin, Campus Virchow-Klinikum, Germany. |
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| Abstract: | Class I alpha-mannosidases are thought to exist exclusively as integral membrane proteins that play intracellulary an essential role in the N-glycan biosynthesis. Using 3H]Man9GlcNAc2 as a substrate, we were able to identify a soluble alpha-mannosidase in human serum that trims the substrate Man9GlcNAc2 to Man(5-8)GlcNAc2 with Man6GlcNAc2 being the major product. This serum mannosidase is Ca2+-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 Man9-mannosidase. |
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