Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA.
Department of Biological Chemistry, Medical School, University of Michigan, Ann Arbor, MI 48109, USA.
J Inorg Biochem. 2022 Nov;236:111949. doi: 10.1016/j.jinorgbio.2022.111949. Epub 2022 Jul 30.
While monitoring the reaction of ferric cytochrome P450cam (Cyp101) with substituted peroxybenzoic acids using rapid-scanning, stopped-flow (RSSF) spectroscopy, an intermediate appears en route to formation of the high-valent moiety known as Compound I [Fe(IV)=O/porphyrin radical cation] that is thought to be the key catalytic species for O-atom transfer to substrate. We have previously suggested (Spolitak, T., Dawson, J.H., Ballou, D.P., J. Biol. Chem.2005, 280, 20,300-20,309) that this species is an acylperoxo-ferric heme adduct that subsequently undergoes OO bond cleavage to generate Compound I. Singular value decomposition analysis of the RSSF data for formation of this intermediate shows that the energy of its Soret absorption peak is sensitive to the electron donor properties of the aryl substituents on the peracid. A linear Hammett correlation plot is seen for the energy of the Soret absorption peak vs. the Hammett σ constant. This correlation requires that the aryl substituents remain as part of the ligand bound to the heme iron, providing direct evidence that the adduct is indeed a ferric acylperoxo derivative. Linear Hammett correlation plots are also seen for both the rate of formation of the intermediate as well as for its conversion to Compound I. It is proposed that the electron donating/withdrawing properties of the aryl-bound substituents affect the electrophilic nature for binding substrate, changing the observed rate of formation for the acylperoxo intermediate, as well as the propensity and stability of the substituted benzoic acid to serve as the leaving group during OO bond cleavage yielding Compound I.
在用快速扫描、停流（RSSF）光谱监测取代过氧苯甲酸与亚铁细胞色素 P450cam（Cyp101）的反应时，出现了一种中间体，该中间体是形成高价部分（称为化合物 I [Fe(IV)=O/卟啉自由基阳离子]）的中间产物，被认为是向底物进行氧原子转移的关键催化物质。我们之前曾提出（Spolitak，T.，Dawson，J.H.，Ballou，D.P.，J. Biol. Chem.2005, 280, 20,300-20,309），该物质是酰基过氧-亚铁血红素加合物，随后进行 OO 键断裂以生成化合物 I。对形成该中间体的 RSSF 数据进行奇异值分解分析表明，其 Soret 吸收峰的能量对过氧苯甲酸的芳基取代基的电子供体性质敏感。可以看到 Soret 吸收峰的能量与 Hammett σ常数之间存在线性 Hammett 相关图。该相关性要求芳基取代基作为与血红素铁结合的配体的一部分保留，这直接证明了加合物确实是一种铁酰基过氧衍生物。也可以看到形成中间体的速率以及中间体向化合物 I 的转化的线性 Hammett 相关图。提出芳基取代基的供电子/吸电子性质影响与底物结合的亲电性，改变酰基过氧中间体的观察形成速率，以及取代苯甲酸作为 OO 键断裂生成化合物 I 的离去基团的倾向和稳定性。
