PMID: 7372668May 10, 1980

On the mechanism of action of cytochrome P-450. Spectral intermediates in the reaction of P-450LM2 with peroxy compounds.

The Journal of Biological Chemistry
R C Blake, M J Coon


In previous studies in this laboratory, highly purified liver microsomal cytochrome P-450 was shown to catalyze the hydroperoxide-dependent hydroxylation of a variety of substrates in the absence of NADPH, NADPH-cytochrome P-450 reductase, and molecular oxygen, and evidence was obtained that the oxygen atom in the product was derived from the peroxide. To determine whether the cytochrome functions in such reactions by a peroxidase-type mechanism, the kinetics of its interactions with a variety of substituted hydroperoxides and peroxy acids have been determined by stopped flow spectrophotometry. The reaction of P-450LM2 with various peroxy compounds yields an intermediate with an absorption maximum at about 436 nm in the difference spectrum, with pseudo-first order or biphasic kinetics depending upon the individual rate constants and the concentration of the oxidant used. The results are in accord with a reversible two-step mechanism, as follows: P-450 + oxidant in equilibrium C in equilibrium D, where C represents a transient intermediate which is detected spectrally only under certain conditions and is probably an enzyme . oxidant complex, and D is the complex with an absorption maximum at about 436 nm in the difference spectr...Continue Reading

Related Concepts

Cytochrome P-450 Oxygenase
Hydrogen-Ion Concentration
Microsomes, Liver

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