Multiple forms of glucose oxidase with different carbohydrate compositions.

A glucose oxidase (beta-D-glucose:oxygen 1-oxidoreductase, EC 1.1.3.4) sample purified from Aspergillus niger by a previously reported method was subjected to isoelectric focusing and gel electrophoresis, and found to be composed of at least six component enzymes. The isoelectric points of the component enzymes ranged from pH 3.9 to 4.3. Analyses of the enzymes indicated that they all possess an identical protein moiety, since the amino acid compositions, the C-terminal sequences, the catalytic parameters, the quantitative and qualitative immunological properties and the electrophoretic patterns of the peptide fragments, obtained by the CNBr-cleavage, were practically the same. On the other hand, the carbohydrate contents of the isolated component enzymes were found to be different, and these differences were associated in the main with a particular peptide fragment. We suggest that the multiplicity of the enzyme is due to variation in the carbohydrate and their structures, rather than in the protein moiety.