Studies on carbohydrate moieties of Aspergillus niger glucoamylase. II: Isolation, purification and characterization of glycopeptides

Abstract

Six glycopeptide fractions namely GP-C₁, GP-C₂, GP-C_3a, GP-C_3b, GP-D, and GP-D₂ were isolated after exhaustive digestion of glucoamylase II (Glucozyme) from Aspergillus niger with pronase. They were purified using gel-filtration. high-voltage paper electrophoresis and ion-exchange chromatography on Dowex-50 and Dowex-1. They appeared homogeneous on electrophoresis under different conditions of pHs. The molecular weights ranged from 1600 and 4000 for these glycopeptides. Ally of them contained serine at the N-terminal end. Serine and threonine were the major amino acids with glycine, alanine, proline and tryosine present as minor constituents. Carbohydrate analysis revealed the presence of different sugars. Based on this, the glycopeptides were grouped into three types: (1) GP-C₁ and GP-C₂ containing mannose, glucose and galactose; (2) GP-C_3a, and GP-C_3b,containing mannose glucose and glucosamine; and (3) GP-D₁ and GP-D₂, containing mannose. glucose, galactose and xylose. Most sugar constituents in each glycopeptide occured in non-integral ratios implying a microheterogeneity of the carbohydrate moiety in Aspergillus niger glucoamylase II.