title: Purification and comparison of the structures of human liver acidic alpha-D-mannosidases A and B.
abstract: Human liver alpha-D-mannosidases A and B were purified 11 500-fold and 2000-fold respectively. Both showed microheterogeneity when analysed by isoelectric focusing. Alpha-D-Mannosidases A and B are immunologically identical but differ in their range of pI values, molecular masses, uptake into fibroblasts and subunit compositions. Alpha-D-Mannosidase A consists of equimolar proportions of subunits of molecular masses 62 kDa and 26 kDa, which are linked by disulphide bridges in the intact enzyme. Alpha-D-Mannosidase B also contains a small subunit, of molecular mass 26 kDa, and a variable mixture of larger subunits, of molecular masses 58 kDa and 62 kDa. The 62 kDa and 58 kDa subunits, but not the 26 kDa one, contain concanavalin A-recognizing glycans. The 58 kDa subunit has a lower pI, contains less high-mannose glycans but probably contains more mannose 6-phosphate than the 62 kDa subunit. It is postulated that the differences in structure and properties of alpha-D-mannosidases A and B are due to differences in the state of processing of the large subunit. This suggestion is consistent with a single locus on chromosome 19 for lysosomal alpha-D-mannosidase.
mesh_terms: D002241:Carbohydrates / Q000032:analysis; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008361:Mannosidases / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D043323:alpha-Mannosidase
chemical_list: D002241:Carbohydrates; D007527:Isoenzymes; D008361:Mannosidases; D043323:alpha-Mannosidase