STABILITY OF A PSEUDOMONAS SP LIPASE - COMPARISON BETWEEN SOLUBILIZEDENZYME IN REVERSE MICELLES AND SUSPENDED LIPASE IN DRY SOLVENTS

The stability of a relatively hydrophobic lipase from Pseudomonas sp., solubilized in reverse micellar media or suspended in dry solvents, w as studied and compared. Factors such as the enzyme-solvent interactio n, enzyme environment, hydration degree of the system, interphase qual ity, droplet size, and water activity were studied. A mixed micellar s ystem which stabilized the lipase is reported. In the case of simple A OT micelles, lipase destabilization with respect to water in small dro plet sizes and stabilization in the biggest micelles was observed. The se effects resulted from lipase penetration into the interphase of the smaller nanodroplets, and the restriction of its conformational mobil ity in the region of structured water of the largest micelles, respect ively. Mixed micelles increased lipase stability, which was mainly rel ated to increased droplet size. Modification with polyethylene glycol decreased lipase stability in reverse micelles, due to the greater int eraction with the micellar interphase. The preparation of nanodroplets , in which native and modified lipases were 5.4 and 9.4 times, respect ively, more stable than in water, is reported. In contrast to the mice llar media, low water contents (low A(w) values) stabilized the solid lipase suspended in organic solvent systems. Under the hydration condi tions studied here,lipase stability increased when more polar solvents were used. Two alternatives were necessary to obtain similar stabilit ies in n-heptane as compared with polar solvents: reduction of the wat er content or use of a low aquaphilic support. The reasons for the dif ferent lipase stabilities in reverse micellar media and solid suspensi ons are discussed.