Purification and stability of a basic peroxidase from strawberry callus culture

A basic isoperoxidase from strawberry (Fragaria × ananassa cv. Chandler) callus culture was purified by sequential CM-Cellulose, Concanavalin-A Sepharose 4B and Sephacryl S-200 chromatographies. Isoelectrofocusing of the purified peroxidase activity revealed the presence of one unique basic isoperoxidase (Faprx1, pI 9.2). Native cathodic electrophoresis and SDS-PAGE analysis of the basic isoenzyme yielded a single protein band. The molecular mass of the basic isoenzyme estimated by SDS-PAGE and matrix-assisted laser desorption ionisation time-of-flight (MALDI-TOF) mass spectrometry was 35 and 32.6 kDa, respectively. The low molecular mass of the isoenzyme may be due to the low degree of glycosylation of its polypeptide chain. Faprx1 showed unusual instability even at room temperature. The effects of bovine serum albumin (BSA), Ca2+, hematin and pH on the stability of the basic isoperoxidase were assayed. The presence of the three stabilising agents showed a remarkable protective effect on Faprx1 activity in a wide pH range.