Oxygenation, and Carbonylation, of a Reduced P450cam Enzyme and Derivatives Reconstituted with Meso-, Deutero-, Dibromodeutero-, and Diacetyldeuteroheme
David Dolphin, James, B.R., and Welborn, H.C.
J. Mol. Catal.
Some thermodynamic data are presented for the oxygenation, and carbonylation, of P. putida cytochrome P450cam systems containing proto-, meso-, deutero-, dibromodeutero-, and diacetyldeutero-porphyrinatoiron(II) centers; the oxidized and 1-electron-reduced states of the enzyme are thought to contain axially bonded cysteine thiolate. Binding of the gases is generally enhanced with the more basic porphyrin systems. Autoxidation of the substrate-bound oxygenated species to superoxide and high-spin Fe(III) follows the rate law k[P450Fe2+(O2)][H+] from pH 7.00 to 8.50, and k also increases with porphyrin basicity. Data for binding of CO, and some autoxidation rates, are also given for some substrate-free systems. Some thermodynamic and kinetic data for reversible oxygenation and carbonylation of protoporphyrin IX-P450 and -myoglobin are compared; weaker CO binding in P450 appears to result form a faster off-rate, whereas weaker O2 binding is reflected in a lower on-rate.