Mechanism of phosphatidylinositol-specific phospholipase C: origin of unusually high nonbridging thio effects

The Arg69 residue in phosphatidylinositol-specific phospholipase C not only binds the phosphate but positions it close to the 2-OH group of inositol in proper alignment for nucleophilic attack. The bidentate nature of this residue produces the large thio effects and stereoselectivity seen in this enzyme.