Part I. Mechanistic and kinetic studies of the oxygenation of modified camphor analogues by cytochrome P450-CAM. Part II. Magnetic circular dichroism and electron paramagnetic resonance spectroscopies as probes of the coordination structures of heme-conta

art I. Several analogues of 1R-camphor, have been synthesized in which the normal hydroxylation site (C-5) by cytochrome P450-CAM is blocked or derivatized with methylenyl or fluorine substituents. Using NADH as the electron donor and putidaredoxin reductase and putidaredowin as electron carriers, these substrates decrease the rate of oxygenated product formation up to 210-fold. An intermolecular isotope effect of 11.7 has been seen for oxygenation of C-9 in 5,5-difluorocamphor. The decrease in optimized turnover number and the large intermolecular isotope effect for substrate hydroxylation observed with these modified substrates suggests that the rate limiting step in the P450 reaction cycle has switched from electron to oxygen transfer. Consequently, the kinetics of hydroxylation of the slow substrates have been examined using rapid-scanning absorption spectroscopy. Experiments have employed meta-chloroperoxybenzoic acid (m-CPBA) as an artificial oxygen donor. We have confirmed the report that addition of m-CPBA to substrate-free ferric P450-CAM leads to transient formation of an intermediate that spectroscopically resembles chloroperoxidase Compound I. Using the slow camphor analogues, this same intermediate is observed in the presence of substrate for the first time.;Part II. Electron paramagnetic resonance spectroscopy (EPR) has been employed to study a series of ferric low-spin derivatives of myoglobin in which the natural prosthetic group, iron protoporphyrin IX, has been replaced with iron heme...