J. Biol. Chem., Vol. 260, Issue 6, 3330-3336, 03, 1985
Branchpoint for heme alkylation and metabolite formation in the oxidation of arylacetylenes by cytochrome P-450
PR Ortiz de Montellano and EA Komives
Phenylacetylene and biphenylacetylene are oxidized by cytochrome P-450 to
the corresponding arylacetic acids. The acetylenic hydrogen shifts to the
adjacent carbon and one atom of molecular oxygen is incorporated into the
carboxylic acid group in these transformations, which are subject to a
large kinetic isotope effect when the acetylenic hydrogen is replaced by
deuterium. The same products and isotope effects are observed when the two
arylacetylenes are oxidized by m-chloroperbenzoic acid rather than by the
enzyme. In contrast, the inactivation of cytochrome P-450 that occurs
during the oxidation of phenylacetylene is insensitive to deuterium
substitution. The partition ratio between metabolite formation and enzyme
inactivation consequently changes from 26 to 15 in going from
phenylacetylene to the deuterated analogue. Metabolite formation therefore
diverges from heme alkylation very early in the catalytic process.