Komives E A, Ortiz de Montellano P R
J Biol Chem. 1987 Jul 15;262(20):9793-802.
Substituted phenylacetylenes are oxidized by purified reconstituted rat liver cytochrome P-450b to the corresponding 2-arylacetic acids. A linear free energy correlation with a rho value of -2.2 exists between the rates of formation of the arylacetic acids and the substituent sigma constants. The enzyme is simultaneously inactivated but the inactivation rates, in contrast to those of metabolite formation, are essentially identical for all the phenylacetylenes. Inactivation is thus insensitive to the electronic nature of the substituents. The metabolite: inactivation ratio consequently decreases from 38 for p-methylphenylacetylene to 4 for p-nitrophenylacetylene. Replacement of the terminal proton of phenylacetylene with deuterium gives rise to an isotope effect of 1.7 on metabolite formation without altering enzyme inactivation. The differential effect of substituents on heme alkylation and metabolite formation requires the two pathways to diverge early in the catalytic process and argues against mechanisms that involve radical cation intermediates.
取代苯乙炔被纯化的重组大鼠肝细胞色素P - 450b氧化为相应的2 - 芳基乙酸。芳基乙酸的生成速率与取代基的σ常数之间存在线性自由能关系，ρ值为 - 2.2。该酶同时失活，但与代谢物形成的速率不同，所有苯乙炔的失活速率基本相同。因此，失活对取代基的电子性质不敏感。代谢物与失活的比率因此从对甲基苯乙炔的38降至对硝基苯乙炔的4。用氘取代苯乙炔的末端质子会对代谢物形成产生1.7的同位素效应，而不会改变酶的失活。取代基对血红素烷基化和代谢物形成的差异效应要求这两条途径在催化过程的早期就分道扬镳，这与涉及自由基阳离子中间体的机制相悖。
