Proximal Ligand Electron Donation and Reactivity of the Cytochrome P450 Ferric鈥揚eroxo Anion
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- 作者：Santhosh Sivaramakrishnan ; Hugues Ouellet ; Hirotoshi Matsumura ; Shenheng Guan ; Pierre Mo毛nne-Loccoz ; Alma L. Burlingame ; Paul R. Ortiz de Montellano
- 刊名：The Journal of the American Chemical Society
- 出版年：2012
- 出版时间：April 18, 2012
- 年：2012
- 卷：134
- 期：15
- 页码：6673-6684
- 全文大小：584K
- 年卷期：v.134,no.15(April 18, 2012)
- ISSN：1520-5126
文摘
CYP125 from Mycobacterium tuberculosis catalyzes sequential oxidation of the cholesterol side-chain terminal methyl group to the alcohol, aldehyde, and finally acid. Here, we demonstrate that CYP125 simultaneously catalyzes the formation of five other products, all of which result from deformylation of the sterol side chain. The aldehyde intermediate is shown to be the precursor of both the conventional acid metabolite and the five deformylation products. The acid arises by protonation of the ferric鈥損eroxo anion species and formation of the ferryl鈥搊xene species, also known as Compound I, followed by hydrogen abstraction and oxygen transfer. The deformylation products arise by addition of the same ferric鈥損eroxo anion to the aldehyde intermediate to give a peroxyhemiacetal that leads to C鈥揅 bond cleavage. This bifurcation of the catalytic sequence has allowed us to examine the effect of electron donation by the proximal ligand on the properties of the ferric鈥損eroxo anion. Replacement of the cysteine thiolate iron ligand by a selenocysteine results in UV鈥搗is, EPR, and resonance Raman spectral changes indicative of an increased electron donation from the proximal selenolate ligand to the iron. Analysis of the product distribution in the reaction of the selenocysteine substituted enzyme reveals a gain in the formation of the acid (Compound I pathway) at the expense of deformylation products. These observations are consistent with an increase in the pKa of the ferric鈥損eroxo anion, which favors its protonation and, therefore, Compound I formation.