XAS STUDIES OF NITRATE REDUCTASE

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。硝酸还原酶（NRs）是由独特的吡蝶呤辅助因子协调的单核钼酶。具有结构特征的nr具有不同的位点，但都具有相同的功能。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先前已用于鉴定拟南芥的同化NR。这表明在催化翻转过程中，相对于Mo-O， Mo-S从反式到顺式发生了意想不到的变化。EXAFS结果也报道了penplasmic NR来自pantotrophus副球菌和P.反硝化。这三个不同的NR位点只有一个共同的Mo=O。鉴于这种可变性，对S. Barnesii的NR进行XAS研究是很重要的，因为它属于系统发育树的不同分支。我们将研究分离状态、硝酸氧化状态、完全还原状态和单电子还原Mo(V)状态下的酶。

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.