Paris Jared C, Nguyen Joline, Kim Hyung J, Hendrich Michael P
Department of Chemistry, Carnegie Mellon University 4400 Fifth Ave. Pittsburgh PA 15213 USA
Division of Physical Sciences, Chemistry, University of Washington Bothell Bothell Washington 98012 USA.
Chem Sci. 2025 Jul 28. doi: 10.1039/d5sc03378k.
Compound 1 is a key intermediate in a large group of enzymes containing heme including cytochromes (cyt) P450, peroxidases and catalases. The extreme reactivity of this highly oxidized species has made its trapping and characterization challenging. Cyt ' of the ammonia-oxidizing bacterium is an enzyme containing heme and a member of the P460 superfamily of cytochromes. Herein, a compound 1 species within the P460 superfamily was trapped and spectroscopically characterized with stopped-flow absorption, EPR and variable-field Mössbauer spectroscopy. Like horseradish peroxidase (HRP), Cyt ' has an axial His coordinated to the heme iron with the compound 1 species exhibiting a green color with an absorption spectrum similar to that of HRP. Compound 1 from Cyt ' features an antiferromagnetic exchange coupling between an = 1 iron(iv)-oxo center and an = ½ porphyrin radical, but with an exchange coupling constant that is significantly greater than that for HRP. The large variation in the exchange constant for both enzymes, despite both having the same axial ligand, indicates that this value is not strongly correlated to the axial ligand identity. Although the reaction of Cyt ' with HO was found to be significantly slower than other peroxidases, the lifetime of the compound 1 species was comparable to other heme enzymes that oxidize a variety of substrates, suggesting that the function of cyt ' may not be relegated solely to the clearance of HO. Given its presence in an ammonia-oxidizing bacterium, cyt ' could oxidize nitrogen containing substrates.
化合物1是一大类含血红素的酶中的关键中间体，这些酶包括细胞色素（cyt）P450、过氧化物酶和过氧化氢酶。这种高度氧化的物种具有极高的反应活性，使得对其进行捕获和表征具有挑战性。氨氧化细菌的细胞色素'是一种含血红素的酶，属于细胞色素P460超家族的成员。在此，利用停流吸收光谱、电子顺磁共振（EPR）和可变场穆斯堡尔光谱对P460超家族中的一种化合物1物种进行了捕获和光谱表征。与辣根过氧化物酶（HRP）一样，细胞色素'有一个轴向组氨酸与血红素铁配位，化合物1物种呈现绿色，其吸收光谱与HRP相似。细胞色素'的化合物1在一个S = 1的铁（IV）-氧中心和一个S = 1/2的卟啉自由基之间具有反铁磁交换耦合，但交换耦合常数明显大于HRP的。尽管两种酶具有相同的轴向配体，但它们的交换常数存在很大差异，这表明该值与轴向配体的身份没有很强的相关性。虽然发现细胞色素'与HO的反应明显比其他过氧化物酶慢，但化合物1物种的寿命与其他氧化各种底物的血红素酶相当，这表明细胞色素'的功能可能不仅仅局限于清除HO。鉴于其存在于氨氧化细菌中，细胞色素'可能氧化含氮底物。
