Spacer effects on enzymatic activity of bromelain immobilized onto porous chitosan beads

Abstract

Bromelain was covalently immobilized onto the surface of porous chitosan beads with and without alkyl chain spacers of different lengths. The relative activity of the immobilized bromelain was found to be high toward a small ester substrate, N-benzyl- l-arginine ethyl ester (BAEE), but rather low toward casein, a high molecular weight substrate. Bromelain immobilized with spacer gave an almost constant activity by varying the surface concentration in marked contrast with the immobilized bromelain without spacer whose activity monotonously decreased with decreasing surface concentration. The relative activity of the immobilized bromelain for hydrolysis of a high molecular weight substrate was a strong function of spacer length. The pH, thermal, and storage stabilities of the immobilized bromelain were higher than those of the free bromelain. The bromelain immobilized directly onto the surface of chitosan beads without any spacer gave a higher stability than those immobilized with spacers. The spacer effect on the activity could be explained in terms of flexibility of the immobilized bromelain molecule.