Vega J M, Garrett R H
J Biol Chem. 1975 Oct 25;250(20):7980-9.
The Neurospora crassa assimilatory nitrite reductase (EC 1.6.6.4) catalyzes the NADPH-dependent reduction of nitrite to ammonia, a 6-electron transfer reaction. Highly purified preparations of this enzyme exhibit absorption spectra which suggest the presence of a heme component (wavelength maxima for oxidized senzyme: 390 and 578 nm). There is a close correspondence between nitrite reductase activity and absorbance at 400 nm when partially purified nitrite reductase preparations are subjected to sucrose gradient centrifugation. In addition, a role for an iron component in the formation of active nitrite reductase is indicated by the fact that nitrate-induced production of nitrite reductase activity in Neurospora mycelia in vivo requires the presence of iron in the induction medium. The heme chromophore present in Neurospora nitrite reductase preparations is reducible by NADPH. Complete reduction, however, requires the presence of added FAD. The NADPH-nitrite reductase activity of the enzyme is also dependent upon addition of FAD. A spectrally unique complex is formed between the heme chromophore and nitrite (or a reduction product thereof) when nitrite is added to NADPH-reducted enzyme. Carbon monoxide forms a complex with the heme chromophore of nitrite reductase with an intense alpha-band maximum at 590 nm and a beta-band of lower intensity at 550 nm. CO is an inhibitor of NADPH-nitrite reductase activity. Spectrophotometrically detectable CO complex formation and Co inhibition of enzyme activity share the following properties...
粗糙脉孢菌同化型亚硝酸还原酶（EC 1.6.6.4）催化依赖NADPH的亚硝酸还原为氨的反应，这是一个6电子转移反应。该酶的高度纯化制剂呈现出的吸收光谱表明存在一种血红素成分（氧化酶的波长最大值：390和578 nm）。当部分纯化的亚硝酸还原酶制剂进行蔗糖梯度离心时，亚硝酸还原酶活性与400 nm处的吸光度之间存在密切对应关系。此外，铁成分在活性亚硝酸还原酶形成中的作用通过以下事实得以表明：在体内，硝酸盐诱导粗糙脉孢菌菌丝体中亚硝酸还原酶活性的产生需要诱导培养基中存在铁。粗糙脉孢菌亚硝酸还原酶制剂中存在的血红素发色团可被NADPH还原。然而，完全还原需要添加FAD。该酶的NADPH-亚硝酸还原酶活性也依赖于FAD的添加。当向NADPH还原的酶中添加亚硝酸盐时，血红素发色团与亚硝酸盐（或其还原产物）之间形成一种光谱上独特的复合物。一氧化碳与亚硝酸还原酶的血红素发色团形成复合物，在590 nm处有一个强烈的α带最大值，在550 nm处有一个强度较低的β带。CO是NADPH-亚硝酸还原酶活性的抑制剂。分光光度法可检测到的CO复合物形成和CO对酶活性的抑制具有以下特性……
