Multi-competitive enzymatic reactions in organic media: a simple test for the determination of lipase fatty acid specificity.

Multiple substrate competition was kinetically analyzed to study lipase-catalyzed reactions in organic media. For each substrate, a competitive factor (the ratio of the specificity constants kcat/Km) was measured by reference to the best substrate using a mixture of fatty acid ethyl esters submitted to a solvolysis reaction by n-propanol. A scale of competitive factors was established which quantitatively described the lipase specificity. This principle was applied to the determination of the specificity of four commercial lipase preparations towards fatty acid chain length and degree of unsaturation. The results were not affected by changes in the physicochemical conditions of the reaction (water content, substrate concentration, nature of nucleophile, etc.). The simple test will be a useful tool to characterize lipase specificity.