González Pablo J, Rivas María G, Brondino Carlos D, Bursakov Sergey A, Moura Isabel, Moura José J G
REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516, Caparica, Portugal.
J Biol Inorg Chem. 2006 Jul;11(5):609-16. doi: 10.1007/s00775-006-0110-0. Epub 2006 May 9.
Nitrate reductases are enzymes that catalyze the conversion of nitrate to nitrite. We report here electron paramagnetic resonance (EPR) studies in the periplasmic nitrate reductase isolated from the sulfate-reducing bacteria Desulfovibrio desulfuricans ATCC 27774. This protein, belonging to the dimethyl sulfoxide reductase family of mononuclear Mo-containing enzymes, comprises a single 80-kDa subunit and contains a Mo bis(molybdopterin guanosine dinucleotide) cofactor and a [4Fe-4S] cluster. EPR-monitored redox titrations, carried out with and without nitrate in the potential range from 200 to -500 mV, and EPR studies of the enzyme, in both catalytic and inhibited conditions, reveal distinct types of Mo(V) EPR-active species, which indicates that the Mo site presents high coordination flexibility. These studies show that nitrate modulates the redox properties of the Mo active site, but not those of the [4Fe-4S] center. The possible structures and the role in catalysis of the distinct Mo(V) species detected by EPR are discussed.
硝酸还原酶是催化硝酸盐转化为亚硝酸盐的酶。我们在此报告了对从硫酸盐还原菌脱硫脱硫弧菌ATCC 27774中分离出的周质硝酸还原酶进行的电子顺磁共振（EPR）研究。这种蛋白质属于含单核钼的二甲基亚砜还原酶家族，由一个80 kDa的亚基组成，含有一个钼双（钼蝶呤鸟苷二核苷酸）辅因子和一个[4Fe-4S]簇。在200至-500 mV的电位范围内，在有和没有硝酸盐的情况下进行的EPR监测的氧化还原滴定，以及在催化和抑制条件下对该酶的EPR研究，揭示了不同类型的Mo(V) EPR活性物种，这表明钼位点具有高度的配位灵活性。这些研究表明，硝酸盐调节钼活性位点的氧化还原性质，但不调节[4Fe-4S]中心的氧化还原性质。讨论了通过EPR检测到的不同Mo(V)物种的可能结构及其在催化中的作用。
