Reversible precipitation of proteins on carboxymethyl cellulose

Precipitation, one of the steps used most routinely in protein purification s. suffers from a general lack of selectivity. In an attempt to impart cont rollable selectivity of a definite nature, carboxymethyl cellulose was deve loped as a soluble ion-exchange precipitant for isolation and purification of proteins. Carboxymethyl cellulose was used as a reversibly soluble/insol uble ion exchange matrix, which after binding proteins from 'crude' could b e precipitated quantitatively with a combination of calcium and polyethylen e glycol. The precipitated proteins were recovered by solubilising in a dis sociating buffer devoid of any one or both of the precipitants i.e. calcium and polyethylene glycol; followed by reprecipitating of carboxymethyl cell ulose. Lactoperoxidase was used as a model enzyme and purified from milk wh ey using the proposed system. A purification factor of about four was achie ved in a single step of precipitation with a suitable choice of binding and elution conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.