Einarsson R, Jahr E, Stiber E, Engman L, Lundström H, Andersson L O
Biochim Biophys Acta. 1980 Aug 21;624(2):386-96. doi: 10.1016/0005-2795(80)90080-x.
Antithrombin III has been shown to contain three disulphide bridges. They can be broken by reduction under non-denaturing conditions. The completely reduced and S-carbamidomethylated protein is devoid of thrombin-inhibiting activity and does not bind heparin. However, the immunological reactivity as determined by electroimmunoassay is almost unchanged, indicating that no large conformational changes occur upon cleavage of the disulphide bonds. This is also supported by the observation that the reduced and S-carbamidomethylated protein has the same fluorescence properties as the native protein dichroic spectrum of the native protein shows a pronounced pattern in the near-ultraviolet region, indicating restricted rotation of the aromatic amino acid side chains. This is drastically changed by the reduction and carbamidomethylation. The character of the far-ultraviolet circular dichroic spectrum is similar in the native and reduced S-carbamidomethylated protein. The reduction and S-carbamidomethylation of antithrombin III induces some local changes in the tertiary structure affecting the inhibitor activity, heparin binding and near-ultraviolet circular dichroic spectrum, but do not seem to induce any substantial general conformation change.
抗凝血酶III已被证明含有三个二硫键。在非变性条件下，它们可通过还原作用断裂。完全还原并经S-氨甲酰甲基化的蛋白质失去了凝血酶抑制活性，且不与肝素结合。然而，通过电免疫测定法测定的免疫反应性几乎未变，这表明二硫键断裂后未发生大的构象变化。这一点也得到了以下观察结果的支持：还原并经S-氨甲酰甲基化的蛋白质与天然蛋白质具有相同的荧光特性，天然蛋白质的二色性光谱在近紫外区域呈现出明显的模式，表明芳香族氨基酸侧链的旋转受限。而还原和氨甲酰甲基化会使其发生剧烈变化。在天然和还原并经S-氨甲酰甲基化的蛋白质中，远紫外圆二色光谱的特征相似。抗凝血酶III的还原和S-氨甲酰甲基化会引起三级结构的一些局部变化，影响抑制剂活性、肝素结合及近紫外圆二色光谱，但似乎并未引起任何实质性的整体构象变化。
