Why is there an "inert" metal center in the active site of nitrile hydratase? Reactivity and ligand dissociation from a five-coordinate Co(III) nitrile hydratase model.
Why is there an "inert" metal center in the active site of nitrile hydratase? Reactivity and ligand dissociation from a five-coordinate Co(III) nitrile hydratase model.
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为什么腈水合酶的活性位点有一个“惰性”金属中心？
DOI：
10.1021/ja002642s
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发表时间：
2001
影响因子：
15
通讯作者：
Kovacs,JA
中科院分区：
文献类型：
--
作者：
Shearer,J;Kung,IY;Lovell,S;Kaminsky,W;Kovacs,JA
为了确定取代惰性金属如何在金属酶腈水合酶（NHase）中发挥催化作用，制备了类似于含钴腈水合酶（Co NHase）的活性位点的反应性五配位CoIII硫醇盐络合物（[CoIII（S2 Me 2N 3（Pr，Pr））]（PF 6）（1））。这是筛选的反应性，通过使用低温电子吸收光谱，对一些生物相关的“基板”。它被确定为1将与叠氮化物，硫氰酸盐和氨反应，但对腈，NO和丁酸盐不反应。底物结合1与[CoIII（ADIT 2）]（PF 6）（2）具有相似的光谱和结构性质。配合物2是一个含有硫醇盐和亚胺氮的六配位钴Ⅲ配合物，具有与钴氨酶钴中心相似的性质。底物结合到1是可逆的和温度依赖性，允许叠氮化物和硫氰酸盐结合的热力学参数和配体解离的速率的测定。叠氮化物和硫氰酸盐以反式与硫醇盐结合，并具有相似的熵和吸收率（硫氰酸盐：ΔH= −7.5 ± 1.1 kcal/mol，ΔS= −17.2 ± 3.2 eu;叠氮化物：ΔH= −6.5 ± 1.0 kcal/mol，ΔS= −12.6 ± 2.4 eu）。叠氮化物和硫氰酸盐从金属中心的位移速率也相当（硫氰酸盐的kd=（7.22 ± 0.04）× 10- 1 s-1，叠氮化物的kd =（2.14 ± 0.50）× 10-2s-1），并且比低自旋d 66配位的Co Ⅲ络合物的位移速率快得多.这些速率与类似的Fe（III）络合物的速率相当，表明Co（III）和Fe（III）在这种配体环境中以相当的速率反应。因此，这项研究表明，从低自旋CoIIIcenter在配体环境中，类似于NHase配体位移是不是prohibitivly慢，以禁止在nonredox活性钴金属酶的催化作用。
To determine how a substitutionally inert metal can play a catalytic role in the metalloenzyme nitrile hydratase (NHase), a reactive five-coordinate CoIIIthiolate complex ([CoIII(S2Me2N3(Pr,Pr))](PF6) (1)) that resembles the active site of cobalt containing nitrile hydratase (Co NHase) was prepared. This was screened for reactivity, by using low-temperature electronic absorption spectroscopy, toward a number of biologically relevant “substrates”. It was determined1will react with azide, thiocyanate, and ammonia, but is unreactive toward nitriles, NO, and butyrate. Substrate-bound1has similar spectroscopic and structural properties as [CoIII(ADIT2)](PF6) (2). Complex2is a six-coordinate CoIIIcomplex containingcis-thiolates and imine nitrogens, and has properties similar to the cobalt center of Co NHase. Substrate binding to1is reversible and temperature-dependent, allowing for the determination of the thermodynamic parameters of azide and thiocyanate binding and the rates of ligand dissociation. Azide and thiocyanate bind trans to a thiolate, and with similar entropies and enthalpies (thiocyanate: ΔH= −7.5 ± 1.1 kcal/mol, ΔS= −17.2 ± 3.2 eu; azide: ΔH= −6.5 ± 1.0 kcal/mol, ΔS= −12.6 ± 2.4 eu). The rates of azide and thiocyanate displacement from the metal center are also comparable to one another (kd= (7.22 ± 0.04) × 10-1s-1for thiocyanate andkd= (2.14 ± 0.50) × 10-2s-1for azide), and are considerably faster than one would expect for a low-spin d6six-coordinate CoIIIcomplex. These rates are comparable to those of an analogous Fe(III) complex, demonstrating that Co(III) and Fe(III) react at comparable rates when in this ligand environment. This study therefore indicates that ligand displacement from a low-spin CoIIIcenter in a ligand environment that resembles NHase is not prohibitivly slow so as to disallow catalytic action in nonredox active cobalt metalloenzymes.