The Effects of Surfactants on Lipase-Catalysed Hydrolysis of Esters: Activities and Stereoselectivity

The effect of surfactants on the hydrolysis of prochiral and chiral substrates by crude and purified porcine pancreatic lipase (PPL, EC 3.1.1.3)) has been studied. Rather than accelerating the reactions, surfactants slowed down (“inhibited”) the reactions relative to the rate in the absence of surfactant. Surfactants varied in the extent to which the reaction was inhibited. With the crude enzyme there was a correlation between degree of inhibition and the optical purity of the product of hydrolysis of an achiral diester substrate 1. There was no special effect associated with use of surfactants in the concentration range corresponding to critical micelle formation, nor was there any increase in rate of reaction when stable emulsions were formed by using mixtures of surfactants to generate an appropriate hydrophile-lipophile (HLB) balance. A study of the effect of sodium dodecyl sulphate (SDS) on the hydrolysis of the diester 1 by crude PPL showed that the rate of the reaction steadily decreased with increasing surfactant concentration, but that the optical purity of the product first fell and then rose gain, an effect attributed to the differential denaturing action of the surfactant on at least three hydrolytic enzymes. In general, there would seem to be no advantage to be gained from the use of surfactants in the hydrolysis by PPL of compounds of low water solubility; the use of an immiscible co-solvent is more effective.