Spectral intermediates in the reaction of oxygen with purified liver microsomal cytochrome P-450 |
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Authors: | F. Peter Guengerich David P. Ballou Minor J. Coon |
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Affiliation: | Department of Biological Chemistry Medical School, The University of Michigan Ann Arbor, Michigan 48109 USA |
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Abstract: | Stopped flow spectrophotometry has shown the occurrence of two distinct spectral intermediates in the reaction of oxygen with the reduced form of highly purified cytochrome P-450 from liver microsomes. As indicated by difference spectra, Complex I (with maxima at 430 and 450 nm) is rapidly formed and then decays to form Complex II (with a broad maximum at 440 nm), which resembles the intermediate seen in steady state experiments. In the reaction sequence, P-450LMredComplex I→Complex II→P-450LMox the last step is rate-limiting. The rate of that step is inadequate to account for the known turnover number of the enzyme in benzphetamine hydroxylation unless NADPH-cytochrome P-450 reductase or cytochrome is added. The latter protein does not appear to function as an electron carrier in this process. |
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