XAS STUDIES OF NITRATE REDUCTASE

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 硝酸还原酶（NR）是由独特的吡喃蝶呤辅因子协调的单核钼酶。结构特征的NR具有不同的位点，所有这些位点都实现相同的功能。通过序列分析预测了四种不同类型的活性位点结构。然而，这些需要通过生物物理方法进行验证。XAS以前已被用于表征拟南芥的同化NR。这表明在催化转换过程中，Mo-S相对于Mo-O从反式到顺式发生了意想不到的变化。还报告了来自泛养副球菌和嗜热副球菌的细胞质NR的EXAFS结果。这三个不同的NR位点仅共享共同的Mo=O。考虑到这一变异性，XAS对S. Barnesii属于系统发育树的不同分支，是重要的。我们将研究的酶在作为隔离状态，在硝酸盐氧化状态，在完全还原状态，并在一个电子还原钼（V）的状态。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Nitrate reductases (NRs) are mononuclear molybdenum enzymes coordinated by distinctive pyranopterin cofactors. The structurally characterized NRs have diverse sites, all of which accomplish the same function. Four distinct types of active site structures are predicted by sequence analysis. However, these need to be verified by biophysical methods. XAS has been used previously to characterize assimilatory NR from Arabidopsis Thaliana. This suggested an unexpected change of Mo-S from trans to cis relative to the Mo-O during the catalytic turnover. EXAFS results have also been reported for the penplasmic NR from Paracocus pantotrophus and P. denitrificans. These three different NR sites only share a common Mo=O. Given this demonstrated variability, XAS studies on the NR from S. Barnesii, which belongs to a different branch of the phylogenetic tree, are important. We will study the enzyme in the as-isolated state, in the nitrate oxidized state, in the fully reduced state, and in the one-electron reduced Mo(V) state.