EQUILIBRIA AMONGST DIFFERENT MOLYBDENUM (V)-CONTAINING SPECIES FROM SULFITE OXIDASE - EVIDENCE FOR A HALIDE LIGAND OF MOLYBDENUM IN THE LOW-PH SPECIES
EQUILIBRIA AMONGST DIFFERENT MOLYBDENUM (V)-CONTAINING SPECIES FROM SULFITE OXIDASE - EVIDENCE FOR A HALIDE LIGAND OF MOLYBDENUM IN THE LOW-PH SPECIES
复制标题
DOI：
10.1042/bj2110227
复制
发表时间：
1983-01-01
影响因子：
4.1
通讯作者：
WILKINSON, T
中科院分区：
文献类型：
--
作者：
BRAY, RC;GUTTERIDGE, S;WILKINSON, T
用亚硫酸盐还原酶中钼(V)的EPR研究了在pH 6.2-9.6范围内，氯离子、氟离子和磷酸根离子与[鸡/肝]亚硫酸盐氧化酶钼中心的相互作用。从.apprx记录的EPR谱中进行了详细的研究。120K和更多来自液体样品光谱的有限研究。295K和酶活性测定。低pH和高pH的Mo(V)EPR信号传递物种之间的相互转化[由Lamy等人描述。(1980)]受到氯离子浓度的影响，浓度增加10倍(在.apprx的范围内)。1 mm-100 mm)导致.apprx的增加。1在表观pK中进行pH U的转化。这表明，Cl-是低pH物种的一种成分。为了支持这一点，高浓度的F-改变了EPR谱。部分转化为Mo(V)物种，其中F-取代了Cl-，并表现出A(19F)av的超精细耦合。0.5Mt[毫特斯拉]，表示。提出了高pH和低pH物种之间的相互转化形式：**图形**。没有发现氯离子是酶活性所必需的证据。提供了与低pH值、高pH值以及磷酸盐物种之间的平衡有关的数据。根据pH值和氯离子和H_2PO_4~-的浓度，1、2或全部3种。可能会出现。在质量上，在适当的条件下，磷酸盐物种倾向于取代部分或全部低pH物种。通过计算机程序的定量分析，可以推导出适当的方案，并评估平衡常数。对295K的EPR信号的研究表明，在液体溶液中也有类似的平衡，但常数的值发生了一些变化。讨论了不同状态下钼中心的结构和酶反应的性质。
The interaction of Cl-, F- and phosphate ions with the Mo center of [chicken/liver] sulfite oxidase in the pH range from 6.2-9.6 was studied by EPR of Mo(V) in the enzyme reduced by sulfite. Detailed studies were made from EPR spectra recorded at .apprx. 120 K and more limited studies from spectra of liquid samples at .apprx. 295 K and also from enzyme activity measurements. Interconversion between low-pH and high-pH Mo(V) EPR signal-giving species [described by Lamy et al. (1980)] is influenced by Cl- concentration, a 10-fold increase in concentration (in the range of .apprx. 1 mM-100 mM) causing an increase of .apprx. 1 pH U in the apparent pK for the conversion. This suggests that Cl- is a constituent of the low-pH species. In support of this, high concentrations of F- modified the EPR spectrum. Partial conversion to a Mo(V) species, in which F- has presumably replaced Cl- and showing hyperfine coupling of A(19F)av. 0.5 mT [millitesla], is indicated. It is proposed that interconversion between high-pH and low-pH species is of the form: .**GRAPHIC**. No evidence that Cl- is essential for enzymic activity was found. Data relating to equilibria amongst low-pH, high-pH and also the phosphate species are presented. Depending on pH and on concentrations of Cl- and H2PO4-, 1, 2 or all 3 spp. may be present. Qualitatively, under appropriate conditions, the phosphate species tends to replace some or all of the low-pH species. Quantitative analysis by a computer procedure permitted an appropriate scheme to be deduced and equilibrium constants to be evaluated. Studies on the EPR signals at 295K indicated that similar equilibria applied in liquid solution, but with some changes in the values of the constants. The structure of the Mo center in its various states and the nature of the enzymic reaction are discussed.