Abstract
Using lipid emulsions as well as the monomolecular film technique, we studied some kinetic properties of sardine digestive lipase (SaDL). The pure lipase was able to hydrolyze a triolein emulsion in the absence of any additives and seems therefore to tolerate the accumulation of long free fatty acids at the interface. The kinetic behavior of SaDL can be explained by the high penetration capacity of this enzyme into a lipidic interface. SaDL hydrolyzes efficiently pure tributyrin, in the absence of additives. Subsequently, the sardine lipase is not denaturated at high interfacial energy. A kinetic study of the surface pressure dependency of the regioselectivity of SaDL was performed using an optically pure stereoisomer of diglyceride (1,2-sn-dicaprin) and a prochiral isomer (1,3-sn-dicaprin) that were spread as monomolecular films at the air-water interface. At low surface pressure, SaDL acts preferentially on distal carboxylic ester groups of the diglyceride isomer (1,3-sn-dicaprin) but at high surface pressure, this enzyme prefers adjacent ester groups of the (1,2-sn-dicaprin) isomer. Interestingly, the SaDL was found to hydrolyze efficiently the secondary ester group of a triglyceride analog. This is in line with the fact that SaDL hydrolyzed triolein at the sn-2 position, as shown using the thin-layer chromatography technique. This property is sought for the synthesis of specific triacylglycerol-based compounds, such as structured lipids.
Practical applications: The sardine digestive lipase was found to efficiently hydrolyse the secondary ester group of a triglyceride analogue, a characteristic sought for the synthesis of structured lipids.