Computational approach to solvent-free synthesis of ethyl oleate using Candida rugosa and Candida antarctica B Lipases. I. Interfacial activation and substrate (ethanol, oleic acid) adsorption

This paper presents the results of a MM2 study of the adsorption of oleic acid and ethanol/water in the tunnel and active-site models of lipases from Candida rugosa and Candida antarctica B. The role of an interface polar/no polar in the opening of C. rugosa lipase's lid is also addressed, discussed and analyzed at the level of the conformational changes needed to achieve the lipase open form. The adsorption of oleic acid and alcohols considering C. antarctica B, a lipase not interfacially activated, is also presented. In this case, the tunnel is shorter than in case of C. rugosa lipase. Two different pockets can be visualized at the active site-tunnel model of C. antarctica B lipase: one for the acyl group and another for the alcohol. Wrong location of alcohol and oleic acid severely hinders reaction because it hinders the H-transfer to histidine, a key step in the reaction mechanism. Right location of alcohol decreases the possibility of alcohol inhibition. In the case of C. rugosa, no restrictions for ethanol/water location are found. For that lipase, a second adsorption site for oleic acid (outside the tunnel) is presented. This site is the exit tunnel of the ester product when oleic acid is adsorbed in the tunnel. Experimental results of our own that correlate with this study are presented.