Bacillus cereus phospholipase C: carboxylic acid ester specificity and stereoselectivity

Thiophosphate analogs of phosphatidylcholine have been synthesized with varying structural complexity. These analogs have been used in a continuous spectrophotometric assay for phospholipase C (Bacillus cereus) to estimate the minimal structural requirements associated with the non-polar portion of the substrate phospholipid. The analogs were of three types containing zero, one or two carboxylic acid ester functionalities. The analogs with one or two ester groups acted as substrates for phospholipase C, while those without an ester functionality were not hydrolyzed. The rac-phosphatidylcholine analog with two ester functionalities gave biphasic time-course results, and was subsequently resolved into enantiomers by selective hydrolysis with a sterospecific phospholipase A2 (Crotalus atrox). The enantiomer with R absolute configuration was rapidly hydrolyzed by the phospholipase C while the enantiomer with the S configuration was slowly hydrolyzed after a long induction period. The results suggest that the B. cereus phospholipase C is specific for an ester functionality and is stereoselective for the R absolute configuration at glycerol C-2.