HETEROGENEOUS GLYCOSYLATION OF CATIONIC PEANUT PEROXIDASE

Cationic peanut peroxidase (CPrx) from a cell suspension culture is N-glycosylated at Asn60, Asn144, and Asn185. All three N-glycans are complex type and galactose rich, and show heterogeneity in length and ConA (concanavalin A) binding property. The glycan heterogeneity causes a polymorphism of the enzyme. Based on its behavior on ConA columns, CPrx can be grouped into two fractions: nonbinding (CPrx(-)) and binding (CPrx(+)) types. A synchronously cosecreted beta-galactosidase has been discovered in the culture medium; there are two isozymes of 60 kDa (pI 7.3) and 66 kDa (pI 7.6). This beta-galactosidase has been partially purified by a combination of ion-exchange and size-exclusion chromatographies and preparative isoelectrofocusing. In vitro experiments indicate that the cosecreted beta-galactosidase is able to convert peroxidase from CPrx(-) to CPrx(+) and may, to some extent, contribute to the glycan heterogeneity of peroxidase in the cell culture.