D-dihexanoylphosphatidylcholine is not a pure competitive inhibitor of phospholipase A 2 hydrolysis of L-dihexanoylphosphatidylcholine

Abstract

The inhibition of Crotalus adamanteus phospholipase A 2 hydrolysis of L-dihexanoylphosphatidylcholine by D-dihexanoylphosphatidylcholine was investigated with inhibitor and substrate in the monomeric concentration range. The results showed that the D-enantiomer acts as a partial (not pute) competitive inhibitor of the enzyme. These results suggest that an ESI complex exists, in which hydrolysis of the substrate still occurs. Thus, binding of the D-enantiomer to the enzyme decreases the affinity for the substrate by a factor, α, while V max is unaffected. The value of α was determined to be 4.70 ± 0.14. These findings complicate the use of D-phosphatidylcholines in mixed micelles with the L-enantiomer as a possible method to investigate the mechanism of interfacial activation of this enzyme.