Thermodynamic and Kinetic Studies on the Binding of Nitric Oxide to a New Enzyme Mimic of Cytochrome P450

详细信息    查看全文

• 作者：Alicja Franke ; Natalya Hessenauer-Ilicheva ; Dominik Meyer ; Gra//pubs.acs.org/images/entities/zdot.gif" border="0">yna Stochel ; Wolf-D. Woggon ; Rudi van Eldik
• 刊名：Journal of the American Chemical Society
• 出版年：2006
• 出版时间：October 18, 2006
• 年：2006
• 卷：128
• 期：41
• 页码：13611 - 13624
• 全文大小：327K
• 年卷期：v.128,no.41(October 18, 2006)
• ISSN：1520-5126

文摘

A new model for the P450 enzyme carrying a SO₃^- ligand coordinated to iron(III) (complex 2)reversibly binds NO to yield the nitrosyl adduct. The rate constant for NO binding to 2 in toluene is of thesame order of magnitude as that found for the nitrosylation of the native, substrate-bound form of P450_cam(E·S-P450_cam). Large and negative activation entropy and activation volume values for the binding of NOto complex 2 support a mechanism that is dominated by bond formation with concomitant iron spin changefrom S = ⁵/₂ to S = 0, as proposed for the reaction between NO and E·S-P450_cam. In contrast, the dissociationof NO from 2(NO) was found to be several orders of magnitude faster than the corresponding reaction forthe E·S-P450_cam/NO system. In a coordinating solvent such as methanol, the alcohol coordinates to iron(III) of 2 at the distal position, generating a six-coordinate, high-spin species 5. The reaction of NO with 5in methanol was found to be much slower in comparison to the nitrosylation reaction of 2 in toluene. Thisbehavior can be explained in terms of a mechanism in which methanol must be displaced during Fe-NObond formation. The thermodynamic and kinetic data for NO binding to the new model complexes of P450(2 and 5) are discussed in reference to earlier results obtained for closely related nitrosylation reactions ofcytochrome P450_cam (in the presence and in the absence of the substrate) and a thiolate-ligated iron(III)model complex.