摘要:
(S)- and (R)-nicotine were used to test a theoretical model for the binding and regioselectivity of cytochrome P-450. Theoretical studies predict that the binding of (R)-nicotine will be more favorable than the binding of (S)-nicotine by between 0.400 and 0.600 kcal. A parallel experimental study determined that the binding constants differed by 0.333 kcal. The overall metabolic rate of (R)-nicotine is 1.4-fold faster than (S)-nicotine which is consistent with the predicted difference in binding energy. Product formation is theoretically predicted to occur at a faster rate at the 5' methylene group than at the N-methyl group of the pyrrolidine ring for both enantiomers. This prediction was confirmed by the experimental results. The factors that are important in the differential binding of the two enantiomers are discussed. The agreement between theory and experiment indicates that the force field used in these calculations may be of general applicability for the prediction of the binding of substrates to P-450cam.