STEREOSELECTIVITY OF LIPASES: Hydrolysis of enantiomeric glyceride analogues by gastric and pancreatic lipases, a kinetic study using the monomolecular film technique

Abstract

In the present study, porcine pancreatic lipase (PPL), rabbit gastric lipase (RGL) and humangastric lipase (HGL) stereospecificity towards enantiomeric glyceride derivatives was kinetically investigated using the monomolecular film technique. Pseudoglycerides such as enantiomeric 1(3)-alkyl-2,3(1 ,2)-diacyl-sn-glycerol or enantiomeric 1(3)-alkyl-2-acyl-snglycerol or enantiomeric 1(3)-acyl-2-acylamino-2-deoxy-sn-glycerol were synthesized in order to assess the lipase stereoselectivity during the hydrolysis of either the primary or the secondary ester position of these glycerides analogues. The cleaved acyl moiety was the samein both enantiomers, thereby excluding the possibility of effects occuring dueto fatty acid specificity. We observed a PPL sn-3 stereoselectivity when using the enantiomeric 1(3)-acyl-2-acylamino-2-deoxy-sn-glycerol (diglyceride analogue) which contrasted with the lack ofstereoselectivity observed when using the enantiomeric 1(3)-alkyl- 2,3(1,2)-diacyl-sn-glycerol (triglyceride analogues). The gastric lipases, in contrast to the pancreatic lipase, preferentially catalyse the hydrolysis of the primary sn-3 ester bond of the enantiomeric monoalky] diacylpairtested. From these kinetic data, high hydrolysis rates and no chiral discrimination were observed in the case of RGL, whereas low rates and a clear chiral discrimination was noticed in the case of HGL duringcatalysis of the acyl chain from the secondary ester bond of 1(3)-alkyl-2-acyl enantiomers.It is particulary obviousthat in the case of HGL decreasing the lipid packing increases the lipase sn-3 stereopreference during hydrolysis of the primary ester bond of the enantiomeric 2-acylaminoderivatives (diglyceride analogues).