NEW EVIDENCE FOR DIMERIZATION-DEPENDENCE OF THE ACTIVITY OF CANDIDA-RUGOSA LIPASE

The specific activity of the lipase of Candida rugosa decreases with i ncreasing enzyme concentration even in the presence of soluble substra tes. Data about the hydrolysis of 2-chloropropionic acid ethyl ester ( CPEE) had suggested that this phenomenon may be caused either by dimer ization of the lipase or by adsorption onto the reactor wall. In order to distinguish between both models, experiments were carried out by c hanging not only the enzyme concentration but also the wetted surface area of the reaction vessel. These novel data reveal that wetted glass surfaces are of only minor importance - if any. Thus, the decrease of activity seems to be caused by some kind of dimerization of the lipas e. In addition, it is shown that adsorption onto hydrophobic surfaces can have a dramatic effect on the specific activity. In the presence o f large hydrophobic surface areas the specific activity is found to be almost as high as that observed in the presence of insoluble substrat e. The analysis of a commonly used test system for lipase activity mea surements based on triacetin hydrolysis exhibits a similar activity-en zyme concentration dependence.