Analogue reaction systems of selenate reductase
Analogue reaction systems of selenate reductase
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DOI：
10.1021/ic0521630
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发表时间：
2006-04-03
影响因子：
4.6
通讯作者：
Holm, RH
中科院分区：
文献类型：
--
作者：
Wang, JJ;Tessier, C;Holm, RH
本文利用双金属氧化物（Bis）建立了硒酸还原酶（SeO_（42）- +2 H（+）+2 e（-）-> SeO_（32）- + H_2O）的抑制反应体系。Mo-IV和W-IV的（二硫代戊烯）络合物，基于氧化和还原酶的EXAFS分析结果，最小反应可能是（MoOH）-O-IV + SeO_（42）->（MoO）-O-VI（OH）+SeO_（32）-。合成了四棱锥配合物[M（OMe）（S_2C_2Me_2）（2）]（1-）（M = MO，W）作为还原酶位点的结构类似物。[ML（S_2C_2Me_2）（2）]（1-）/SeO_（42-）（L = OMe，OPh，SC_6H_2 - 2，4，6-Pr-3（i））体系在乙腈中，硒酸盐还原为亚硒酸盐的二级反应，其负活化熵暗示缔合过渡态。298 K时的速率常数在10（-2）-10（-4）M-1 s（-1）范围内，Δ S-双匕首= -12至-34 eu。当速率常数与以前的数据进行比较，减少（CH 2）（4）SO，Ph 3AsO，和硝酸盐的氧原子转移，反应性的趋势依赖于金属，轴向配体L，和基板被确定。与通过氧代转移还原底物的所有其他情况一样，动力学金属效应k（2）（w）> k（2）（Mo）成立。通过合成[Mo-IV（O2 CR）（S2 C2Me 2）（2）]（1-）（R = Ph，Bu '）复合物，从一级序列比对中提出了一个建议，即保守的Asp残基可能是DMSO还原酶家族中11型酶的配体。该物种显示对称的η（2）-羧酸结合和扭曲的三角棱柱立体化学。他们作为可能的结构类似物的硝酸盐，硒酸盐，高氯酸盐还原酶的还原位点下提出的天冬氨酸协调。羧酸结合已被晶体学证明的硝酸还原酶，但不是其他两种酶。
Analogue reaction systems of selenate reductase, which reduces substrate in the overall enzymatic reaction SeO42- + 2H(+) + 2e(-) -> SeO32- + H2O, have been developed using bis(dithiolene) complexes of Mo-IV and W-IV, On the basis of the results of EXAFS analysis of the oxidized and reduced enzyme, the minimal reaction (MoOH)-O-IV + SeO42- -> (MoO)-O-VI(OH) + SeO32- is probable. The square pyramidal complexes [M(OMe)(S2C2Me2)(2)](1-) (M = MO, W) were prepared as structural analogues of the reduced enzyme site. The systems, [ML(S2C2Me2)(2)](1-)/SeO42- (L = OMe, OPh, SC6H2-2,4,6-Pr-3(i)) in acetonitrile, cleanly reduce selenate to selenite in second-order reactions whose negative entropies of activation implicate associative transition states. Rate constants at 298 K are in the 10(-2)-10(-4) M-1 s(-1) range with Delta S-double dagger = -12 to -34 eu. When rate constants are compared with previous data for the reduction of (CH2)(4)SO, Ph3AsO, and nitrate by oxygen atom transfer, reactivity trends dependent on the metal, axial ligand L, and substrate are identified. As in all other cases of substrate reduction by oxo transfer, the kinetic metal effect k(2)(w) > k(2)(Mo) holds. A proposal from primary sequence alignments suggesting that a conserved Asp residue is a likely ligand in the type 11 enzymes in the DMSO reductase family has been pursued by synthesis of the [Mo-IV(O2CR)(S2C2Me2)(2)](1-) (R = Ph, Bu') complexes. The species display symmetrical eta(2)-carboxylate binding and distorted trigonal prismatic stereochemistry. They serve as possible structural analogues of the reduced sites of nitrate, selenate, and perchlorate reductases under the proposed aspartate coordination. Carboxylate binding has been crystallographically demonstrated for one nitrate reductase, but not for the other two enzymes.