Branchpoint for heme alkylation and metabolite formation in the oxidation of arylacetylenes by cytochrome P-450.

P R Ortiz De Montellano,E A Komives

doi:10.1016/s0021-9258(19)83624-4

Abstract

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.

Highlights

Phenylacetylene and biphenylacetylene are oxidized metabolism of biphenylacetylenes (14-19) but is implied by by cytochrome P-450to 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 inactivation of cytochrome P-450that occurs during the oxidation of phenylacetylene is insensitive to deuteriumsubstitution

Summary

THEJOURNAO FLBIOLOGICACL HEMISTRY

0 1985 by The American Society of Biological Chemists, Inc. Vol 260, No 6, Issue of March 25, pp. 33303336.1985 Printed in U.S.A. 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 catalytic oxidation of biphenylacetylene yields biphenylaceticacid in a reaction subject to a kinetic isotope effect of1.4 when the acetylenic hydrogen is replaced by deuterium (19). The possibility that oxygen is inserted into the acetylenic carbonhydrogen bond, suggested by the isotope effect, is ruled out by quantitative shiftof the acetylenic hydrogen to thevicinal carbon during the oxidation (17-19) and by the observation of a similar intramolecular hydrogen shift in the chemical oxidation of biphenylacetylene (17, 18).The enzymatic oxidation of acetylenes, likethat of olefins, involves reaction of the activated oxygen with the *-bond. Retention of the olefin stereochemistry in the epoxidesfavorsa concerted epoxidation mechanism

RESULTS

DISCUSSION

New York

MATERIALS W D METHODS

Findings

Rates Of product formation