L-asparaginase bound to collagen membranes: effect of glutaraldehyde crosslinking on stabilization of catalytic activity

Reconstituted bovine collagen has been used extensively in our laboratory as a carrier for immobilized E. coli L-asparaginase. The activity and catalytic stability of these collagen-asparaginase membranes can be altered substantially by conditions used in membrane crosslinking with glutaraldehyde. As the concentration of glutaraldehyde used in tanning is increased, the initial specific activity of collagen-asparaginase membranes decreased asymptotically to a limiting value. Similar results occurred when membranes were subjected to increasing time periods of tanning at a constant glutaraldehyde concentration. These observations point to a time-concentration relationship for glutaraldehyde tanning and its effect on the specific activity of collagen-asparaginase membranes. Specific activities of membranes tanned a glutaraldehyde concentrations of 5% or higher appear to be very stable over long periods of alternate storage and assay. This result, however, is not observed with membranes tanned at glutaraldehyde concentrations lower than 5% for short periods of time (approximately 30 sec to 1 min). It is not clear whether the instability of membranes tanned at lower concentrations of glutaraldehyde or shorter intervals of tanning is due to enzyme elution from the membrane or denaturation of the bound enzyme.