Effects of water activity on Vmax and KM of lipase catalyzed transesterification in organic media

Summary The V_max and K_M of various forms of lipase from Pseudomonas cepacia (powder, adsorbed onto Celite or covalently linked to polyethylene glycol) were determined in organic solvents preequilibrated to water activities (a_w) from <0.1 to 0.84. The model reaction was the transesterification between n-octanol and vinyl butyrate. It was found that K_M for the nucleophile increased with increasing a_w for all three lipase forms. V_max increased with increasing a_w for polyethylene glycol-lipase, whereas there was an optimum at intermediate a_w values (0.11 – 0.38) for lipase powder and Celite-immobilized lipase.