Titration and assignment of residues that regulate the enantioselectivity of phenylacetone monooxygenase

Phenylacetone monooxygense (PAMO) from Thermobifida fusca was employed for the asymmetric oxidation of thioanisole (sulfooxidation) and of racemic 2-phenylpropionaldehyde (Baeyer-Villiger oxidation). A pH dependence of enantioselectivity was observed in both cases. Two different residues, with pKa values of 7.8±0.2 and 9.2±0.2, appeared to be responsible for the pH effects on PAMO enantioselectivity. The protonation of Arg337 and the FAD:C4a-hydroperoxide/FAD:C4a-peroxide equilibrium were identified as the major factors responsible for the fine-tuning of PAMO enantioselectivity in Baeyer-Villiger oxidation and sulfooxidation, respectively.