Water as a competitive inhibitor of lipase-catalysed esterification in organic media

Kinetic parameters were determined for esterification of dodecanol and decanoic acid in hexane catalysed by lipases from Rhizomucor miehei and Candida rugosa, after pre-equilibration to different values of thermodynamic water activity (aw). Vm increases with increasing aw, but so do the Km values for both substrates. The effect on Km for the alcohol probably represents competition between the first product and the second substrate, as expected for Ping-pong kinetics. The rise in Km for the acid probably reflects the displacement of water molecules during substrate binding.