XAS STUDIES OF NITRATE REDUCTASE

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 硝酸还原酶(NRs)是一种由独特的吡喃蝶呤辅助因子协调的单核钼酶。具有结构特征的NRs具有不同的位置，所有这些位置都完成相同的功能。通过序列分析预测了四种不同类型的活性中心结构。然而，这些都需要通过生物物理方法进行验证。XAS已被用于鉴定拟南芥的同化天然产物。这表明在催化剂周转过程中，相对于Mo-O，Mo-S发生了从反式到顺式的意外变化。EXAFS结果也被报道了来自泛养副中心和脱氮副中心的细胞质NR。这三个不同的NR位点只有一个共同的Mo=O。考虑到这种变异性，对属于系统发育树不同分支的巴氏链霉菌的NR进行XAS研究是很重要的。我们将研究酶在AS隔离状态、硝酸盐氧化状态、完全还原状态和单电子还原Mo(V)状态下的变化。

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.