Preparation and properties of an immobilized derivative of penicillinase.

Penicillinase (beta-lactamase I, EC 3.5.2.6) secreted by Bacillus cereus, strain 569/H, was covalently attached to aminoethyl cellulose via glutaraldehyde. The immobilized derivative shows increased thermostability and decreased susceptibility to conformational changes induced by certain substrates of penicillinase. The decline in the rate of hydrolysis of such substrates was consequently suppressed by immobilization. A marked increase in Km was observed with all substrates except for the unsubstituted 6-aminopenicillanic acid. The altered properties of the new derivative are attributed to the constraint imposed by immobilization on the conformational flexibility of the enzyme molecule. Thus, apart from obvious technological interest, immobilized penicillinase provides a useful model for the study of the role of flexibility in the function of an enzyme.