Kim Sun Hee, Perera Roshan, Hager Lowell P, Dawson John H, Hoffman Brian M
Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA.
J Am Chem Soc. 2006 May 3;128(17):5598-9. doi: 10.1021/ja060776l.
The classical heme-monooxygenase active intermediate, compound I (Cpd-I), incorporates a heme which is oxidized by two equivalents above the resting ferric state, one equivalent associated with a ferryl center, [Fe=O]2+ (FeS = 1), and the other with an active-site radical (RS = 1/2). Theoretical calculations on models of a Cpd-I with a thiolato axial ligand have presented divergent views about its electronic structure. In one picture, the radical is on the porphyrin; in the other, it is on the sulfur. In this report, ENDOR spectroscopy answers the question, does Cpd-I of the enzyme chloroperoxidase contain a porphyrin pi-cation radical or an iron-bound cysteinyl radical: the radical is predominantly on the porphyrin, with spin density on sulfur having an upper bound, rhoS </= rhoSmax approximately 0.23. We further suggest that the same answer applies to Cpd-I of cytochromes P450.
经典的血红素单加氧酶活性中间体化合物I（Cpd-I）包含一个血红素，该血红素在静止的三价铁状态之上被两个当量氧化，一个当量与一个高价铁中心[Fe=O]2+（FeS = 1）相关，另一个与一个活性位点自由基（RS = 1/2）相关。对具有硫醇轴向配体的Cpd-I模型的理论计算对其电子结构提出了不同的观点。在一种情况中，自由基在卟啉上；在另一种情况中，它在硫上。在本报告中，电子核双共振光谱回答了这个问题，即氯过氧化物酶的Cpd-I是否包含一个卟啉π-阳离子自由基或一个与铁结合的半胱氨酰自由基：自由基主要在卟啉上，硫上的自旋密度有一个上限，ρS≤ρSmax约为0.23。我们进一步表明，相同的答案也适用于细胞色素P450的Cpd-I。
