Immobilization of chitinase on a reversibly soluble–insoluble polymer for chitin hydrolysis

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Abstract
Serratia marcescens chitinase was immobilized by covalent binding to a polymer (hydroxypropyl methylcellulose acetate succinate, AS-L) showing reversibly soluble–insoluble characteristics with pH change. The immobilized enzyme (CHAS) was soluble above pH 5·2 and insoluble below 4·5, which offers advantages in that it can carry out hydrolysis of chitin particles in a soluble form yet be recovered after precipitation at low pH. CHAS has much higher activity than chitinase immobilized to a water-insoluble carrier. The effects of pH and temperature on the activity and stability of CHAS, and the adsorption of CHAS to chitin were studied and compared with those of free chitinase. Following repeated pH cycles between 6·6 and 4·5, CHAS lost 30% of its enzyme activity during the first cycle due to protein release and enzyme denaturation, but substantially less activity was lost in the following cycles, with minimum enzyme denaturation. Chitin hydrolysis with CHAS could be carried out in a semi-batch mode with intermittent enzyme precipitation and product removal, this can enhance product yield up to 1·4-fold when compared with batch reaction.