Abstract
The adsorption of proteinase K on Poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) films was studied by contact angle, surface tension and microscopic measurements. Environmental scanning electron microscopie clearly shows that proteinase K can irreversibly adsorb on PLLA film. In contrast, no enzyme adsorption was detected on PDLA film under the same conditions. The contact angle of PLLA film rapidly decreases after immersion in Tris buffer containing proteinase K, whereas that of PDLA remains unchanged. These findings indicate that enzyme adsorption may be a prerequisite for enzymatic degradation of polylactide substrates. Surface tension measurements allow to calculate the average area occupied per proteinase K molecule (ApM). The ApM value was found to be about 46 Ų at 25oC, and 29 Ų at 37oC, suggesting that at higher temperature, enzyme molecules exhibit a more compact conformation.