Pereira I C, Abreu I A, Xavier A V, LeGall J, Teixeira M
Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal.
Biochem Biophys Res Commun. 1996 Jul 25;224(3):611-8. doi: 10.1006/bbrc.1996.1074.
The membrane bound cytochrome c nitrite reductase from the sulfate reducer Desulfovibrio desulfuricans (ATCC 27774) was found to have a high specific activity in the reduction of sulfite, producing stoichiometric amounts of sulfide. The K(m) for sulfite in the MV+.:sulfite oxidoreductase assay is 0.75 mM, and the specific activity 2.06 mumolH2/min/mg. Visible and EPR spectroscopies studies indicate that the enzyme high-spin heme reacts with sulfite in the oxidised state, and that sulfide partially reduces the enzyme. The redoxcycled enzyme, using H2/Hydrogenase/MV+. as a reductant, is identical to the resting enzyme. This is the first time that a c-type nitrite reductase has been shown to reduce sulfite. These findings, besides revealing a new function for the nitrite reductase, raise a major question regarding the sulfur metabolism in the sulfate reducing bacteria as well as the cellular localization of the enzymatic activities involved in the dissimilatory reduction of sulfate. The purified nitrite reductase is a heterooligomer, containing two types of subunits of 62 kDa (+/- 5 kDa) and 18.8 kDa (+/- 1 kDa), and forms a complex or aggregate with a molecular mass of approximately 750 kDa.
研究发现，来自硫酸盐还原菌脱硫脱硫弧菌（ATCC 27774）的膜结合细胞色素c亚硝酸盐还原酶在亚硫酸盐还原反应中具有高比活性，能产生化学计量的硫化物。在MV⁺：亚硫酸盐氧化还原酶测定中，亚硫酸盐的K(m)为0.75 mM，比活性为2.06 μmolH₂/min/mg。可见光谱和电子顺磁共振光谱研究表明，该酶的高自旋血红素在氧化态下与亚硫酸盐反应，且硫化物能部分还原该酶。以H₂/氢化酶/MV⁺作为还原剂的氧化还原循环酶与静止酶相同。这是首次证明c型亚硝酸盐还原酶能还原亚硫酸盐。这些发现除揭示了亚硝酸盐还原酶的新功能外，还引发了关于硫酸盐还原菌中硫代谢以及参与异化硫酸盐还原的酶活性的细胞定位的重大问题。纯化的亚硝酸盐还原酶是一种异源寡聚体，包含两种亚基，分别为62 kDa（±5 kDa）和18.8 kDa（±1 kDa），并形成分子量约为750 kDa的复合物或聚集体。
