Probing the hydrophobic pocket of the active site in the particulate methane monooxygenase (pMMO) from Methylococcus capsulatus (Bath) by variable stereoselective alkane hydroxylation and olefin epoxidation.

摘要: pMMO from M. capsulatus (Bath) oxidizes straight-chain C1-C5 alkanes and alkenes to form their corresponding 2-alcohols epoxides. According experiments performed with cryptically chiral ethane D,L-[2-(2)H(1),3-(2)H(1)]butane, the reactions proceed through concerted O-atom insertion mechanism. However, when propene but-1-ene are used as epoxidation substrates, enantiomeric excesses (ees) of enzymatic products only 18 37 %, respectively. This relatively poor stereoselectivity in presumably reflects low stereochemical differentiation between re si faces hydrophobic pocket active site. Further insights into reaction mechanism now provided by studies on trans-but-2-ene, which reveal D,L-2,3-dimethyloxirane products, cis-but-2-ene, yield meso product. These observations indicate that indeed proceeds electrophilic syn addition. To achieve better facial selectivity, we have also 3,3,3-trifluoroprop-1-ene substrate. The obtained 90 % (2S)-oxirane. When 1,1,1-trifluoropropane is substrate, hydroxylation at 2-carbon exhibits an inverse selectivity relative seen normal butane, if consider size CF(3) group fluorinated propane be comparable one ethyl groups butane. beginning delineate factors influence orientations various substrates cavity site enzyme.