Effects of carbohydrate chain on surface net charge and hydrophobicity of glycoenzymes

Three different carbohydrate-depleted enzymes were prepared from an endo-beta-1,4-glucanase of Aspergillus niger IFO31125 by treatment with endo-beta-N-acetylglucosaminidase or alpha-mannosidase. The molecular sizes of these enzymes decreased from 40 kDa containing about 8.9% carbohydrate to 39, 38, and 37 kDa with carbohydrate at 4.5, 1.3, and 0.8% (w/w), respectively. The surface net charges on these enzyme preparations were calculated from their electrophoretic mobilities measured by capillary zone electrophoresis. They had increased negative charges corresponding to the decreases in the carbohydrate content; those of native and 37-kDa enzymes were about -0.03 and -0.045, respectively. The surface hydrophobicities of proteins were also measured by partitioning the enzymes in a two-phase system containing polyethylene glycol and dextran, and decreased corresponding with decreases in their carbohydrate content. The results indicated that the high mannose type of carbohydrate chain in endo-beta-1,4-glucanase affected the surface net charge on the enzyme and increased the surface hydrophobicity.