Glycoenzymes: an unusual type of glycoprotein structure for a glucoamylase.
Glucoamylase, (1 leads to 4)(1 leads to 6)-alpha-D-glucan glucohydrolase (EC 3.2.1.3), hydrolyzes starch and glycogen completely to D-glucose and is used industrially in the manufacture of D-glucose from starch. The enzyme is elaborated by many types of fungi and occurs in two isoenzymic forms (glucoamylase I and glucoamylase II) in extracts from certain fungi. The isoenzymes from Aspergillus niger are glycoenzymes containing D-mannose, D-glucose, and D-galactose as integral structural components. New data from experiments on reductive alkaline beta-elimination and from methylation analyses show that the carbohydrate chains of glucoamylase I are linked O-glycosidically from D-mannose residues to L-serine or L-threonine residues of the protein moiety. In this enzyme, the carbohydrate residues are present as 20 single D-mannose residues, 11 disaccharides components having the structure 2-O-D-mannopyranosyl-D-mannose, 8 trisaccharides, and 5 tetrasaccharides composed of various combinations of D-mannose, D-glucose, and D-galactose residues joined by (1 leads to 3) and (1 leads to 6) glycosidic linkages. Such an array of carbohydrate chains in a glycoprotein is unusual, and may account for some of the unique properties exhibited by glucoamylase.
D000596:Amino Acids / Q000032:analysis; D001234:Aspergillus niger / Q000201:enzymology; D002241:Carbohydrates / Q000032:analysis; D005087:Glucan 1,4-alpha-Glucosidase; D005959:Glucosidases; D006023:Glycoproteins; D007527:Isoenzymes; D013058:Mass Spectrometry; D008745:Methylation; D011487:Protein Conformation
D000596:Amino Acids; D002241:Carbohydrates; D006023:Glycoproteins; D007527:Isoenzymes; D005959:Glucosidases; D005087:Glucan 1,4-alpha-Glucosidase