Yoneda G S, Mitchel G L, Blackmer G L, Holwerda R A
Bioinorg Chem. 1978;8(5):369-86. doi: 10.1016/s0006-3061(00)80272-0.
Rate parameters are reported for the oxidation of cuprous stellacyanin by Co(PDTA)-(k(25.0 degrees) = 17.9 M(-1)sec(-1), deltaH not equal to = 8.5 kcal/mol, deltaH not equal to = 8.5 kcal/mol, deltaS not equal to = -24 cal/mol-deg; pH 7.0, Mu 0.5 M) and Co(CyDTA)-(k(25.1 degrees) = 17.0 M(-1)sec(-1), deltaH not equal to = 8.7 kcal/mol, deltaS not equal to = -24 cal/mol-deg; pH 7.0 mu 0.5 M). The first order Co(PDTA)- and Co(CyDTA)- dependences observed over wide concentration ranges contrast with the saturation behavior reported previously for Co(EDTA)- as the oxidant. It is concluded that the- CH3 and -(CH2)4-substituents of PDTA and CyDTA, respectively, prevent the alkylated derivatives of Co(EDTA)- from hydrogen bonding with the reduced blue protein, causing precursor complex formation constants to fall far below that of 149M(-1) (25.1 degrees) observed for the EDTA complex. The similarity between deltaH not equal to and deltaS not equal to values for the oxidation of stellacyanin by Co(PDTA)- and Co(CyDTA)- indicates that the size of alkyl substituents linked to the carbon atoms of the EDTA ethylenediamine backbone has little influence on activation requirements for Cu(I) to Co(III) electron transfer. The electron transfer reactivity of aminopolycarboxylatocobalt(III) complexes with cuprous stellacyanin therefore appears to be linked to the accessibility of one or more of the ligated acetate groups to outer-sphere contact with the type 1 Cu(I) center. Saturation in kobsd vs. [oxidant] plots found for the reactions of Co(PDTA)- and Co(CyDTA)- with stellacyanin at pH 6 and at pH 7 in the presence of EDTA is attributed to the formation of "dead-end" oxidant-protein complexes.
报道了钴（PDTA）（25.0℃时k = 17.9 M⁻¹sec⁻¹，ΔH≠ = 8.5 kcal/mol，ΔH≠ = 8.5 kcal/mol，ΔS≠ = -24 cal/mol·deg；pH 7.0，μ = 0.5 M）和钴（CyDTA）（25.1℃时k = 17.0 M⁻¹sec⁻¹，ΔH≠ = 8.7 kcal/mol，ΔS≠ = -24 cal/mol·deg；pH 7.0，μ = 0.5 M）氧化亚铜星蓝蛋白的速率参数。在很宽的浓度范围内观察到的一级钴（PDTA）和钴（CyDTA）依赖性与先前报道的以钴（EDTA）作为氧化剂时的饱和行为形成对比。得出的结论是，PDTA和CyDTA的-CH₃和-(CH₂)₄取代基分别阻止了钴（EDTA）的烷基化衍生物与还原态蓝色蛋白形成氢键，导致前体配合物形成常数远低于EDTA配合物所观察到的149 M⁻¹（25.1℃）。钴（PDTA）和钴（CyDTA）氧化星蓝蛋白时的ΔH≠和ΔS≠值之间的相似性表明，与EDTA乙二胺主链碳原子相连的烷基取代基的大小对Cu(I)到Co(III)电子转移的活化要求影响很小。因此，氨基多羧基钴（III）配合物与亚铜星蓝蛋白的电子转移反应性似乎与一个或多个连接的乙酸根基团与1型Cu(I)中心进行外层接触的可及性有关。在pH 6和pH 7且存在EDTA的情况下，钴（PDTA）和钴（CyDTA）与星蓝蛋白反应的kobsd对[氧化剂]图中的饱和现象归因于“终止”氧化剂-蛋白配合物的形成。
