Olivas E, De Waal D J, Wilkins R G
J Biol Chem. 1977 Jun 25;252(12):4038-42.
The rate constants for reduction by dithionite of a number of metmyoglobin species Mb+X(X=H2O, imidazole, OH-, F-, N3-, CNO-, SCN-, HCO2-, NO2-, and CN-) were measured at 25 degrees by stopped flow spectrophotometry. The dependence of the rate was [S2O42-]1/2, and the SO2- radical was considered to be the active reductant. Except for X=imidazole and CN-, reduction occurred through dissociation of Mb+X. Values for the dissociative rate constant obtained from dithionite reduction were in good agreement with those obtained directly. Reduction of the dissociated fragment (assumed Mb+H2O) by SO2- is 3+/-1 X 10(6) M-1S-1 at pH 8.2 for all Mb+X species examined. Reduction of Mb+ imidazole and Mb+CN- occurs directly with SO2-, and Mb0CN- (Mb0, deoxymyoglobin) is characterized as an intermediate in reduction of the latter.
在25摄氏度下，通过停流分光光度法测量了连二亚硫酸盐对多种高铁肌红蛋白物种（Mb+X，其中X = H₂O、咪唑、OH⁻、F⁻、N₃⁻、CNO⁻、SCN⁻、HCO₂⁻、NO₂⁻和CN⁻）的还原速率常数。速率对[S₂O₄²⁻]的依赖关系为[S₂O₄²⁻]¹/²，并且认为SO₂⁻自由基是活性还原剂。除了X = 咪唑和CN⁻外，还原是通过Mb+X的解离发生的。从连二亚硫酸盐还原获得的解离速率常数的值与直接获得的值非常一致。对于所有检测的Mb+X物种，在pH 8.2时，SO₂⁻对解离片段（假设为Mb+H₂O）的还原速率为3±1×10⁶ M⁻¹S⁻¹。Mb+咪唑和Mb+CN⁻与SO₂⁻直接发生还原反应，并且Mb⁰CN⁻（Mb⁰，脱氧肌红蛋白）被表征为后者还原过程中的中间体。
