Dipartimento di Scienze Biochimiche A. Rossi Fanelli, Sapienza-Università di Roma, Rome, Italy.
Biochem Soc Trans. 2011 Jan;39(1):195-200. doi: 10.1042/BST0390195.
The cd1 NiRs (nitrite reductases) are enzymes catalysing the reduction of nitrite to NO (nitric oxide) in the bacterial energy conversion denitrification process. These enzymes contain two distinct redox centres: one covalently bound c-haem, which is reduced by external electron donors, and another peculiar porphyrin, the d1-haem (3,8-dioxo-17-acrylate-porphyrindione), where nitrite is reduced to NO. In the present paper, we summarize the most recent results on the mechanism of nitrite reduction by the cd1 NiR from Pseudomonas aeruginosa. We discuss the essential catalytic features of this enzyme, with special attention to the allosteric regulation of the enzyme's activity and to the mechanism employed to avoid product inhibition, i.e. trapping of the active-site reduced haem by the product NO. These results shed light on the reactivity of cd1 NiRs and assign a central role to the unique d1-haem, present only in this class of enzymes.
cd1 型亚硝酸盐还原酶（nitrite reductases）是一种酶，能够在细菌能量转换反硝化过程中催化将亚硝酸盐还原为一氧化氮（nitric oxide）。这些酶包含两个截然不同的氧化还原中心：一个共价结合的 c-卟啉环，可被外部电子供体还原，另一个特殊的卟啉环，即 d1-卟啉环（3,8-二氧代-17-丙烯酰基卟啉二酮），其中亚硝酸盐被还原为 NO。在本文中，我们总结了铜绿假单胞菌 cd1 型亚硝酸盐还原酶还原亚硝酸盐的最新机制研究结果。我们讨论了该酶的关键催化特征，特别关注酶活性的变构调节，以及用于避免产物抑制的机制，即通过产物 NO 捕获活性位点还原的血红素。这些结果阐明了 cd1 型亚硝酸盐还原酶的反应性，并赋予了仅存在于此类酶中的独特 d1-卟啉环核心作用。
