Murphy M J, Siegel L M, Tove S R, Kamin H
Proc Natl Acad Sci U S A. 1974 Mar;71(3):612-6. doi: 10.1073/pnas.71.3.612.
Ferredoxin-nitrite reductase (EC 1.7.7.1) of spinach, an enzyme that catalyzes the six-electron reduction of nitrite to ammonia, contains siroheme, the new type of prosthetic group recently found in several sulfite reductases (both assimilatory and dissimilatory) that can catalyze the reduction of sulfite to sulfide, also a six-electron reduction. The prosthetic group of sulfite reductase had previously been shown to be an iron-tetrahydroporphyrin of the isobacteriochlorin type (adjacent pyrrole rings reduced) with eight carboxylate side chains. This finding suggests that both types of "multi-electron" reduction processes may share common mechanistic features.
菠菜中的铁氧化还原蛋白-亚硝酸还原酶（EC 1.7.7.1）是一种催化将亚硝酸盐六电子还原为氨的酶，它含有西罗血红素，这是最近在几种亚硫酸盐还原酶（同化型和异化型）中发现的新型辅基，这些亚硫酸盐还原酶能催化亚硫酸盐还原为硫化物，也是一个六电子还原过程。此前已证明亚硫酸盐还原酶的辅基是异菌叶绿素类型的铁四氢卟啉（相邻吡咯环还原），带有八个羧酸盐侧链。这一发现表明，这两种类型的“多电子”还原过程可能具有共同的机制特征。
