Darawshe S, Millar D B, Ahmed S A, Miles E W, Minton A P
Section on Physical Biochemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0830, USA.
Biophys Chem. 1997 Nov;69(1):53-62. doi: 10.1016/s0301-4622(97)00078-1.
The dissociation equilibria of Salmonella typhimurium tryptophan synthase alpha 2 beta 2 complex were studied via centrifugation of the complex to sedimentation equilibrium in neutral saline buffers containing 0 to 137 mM guanidine isothiocyanate (GuSCN). The resulting concentration gradients were analyzed in the context of an equilibrium model for sequential dissociation of two alpha subunits from a stable beta 2 subunit. Under the conditions of these experiments, the first dissociation constant alone could be evaluated at GuSCN concentrations < or = 100 mM, and the second dissociation constant alone could be evaluated at GuSCN = 137 mM. At intermediate GuSCN, both dissociation constants were sufficiently well defined to rule out the presence of a large equilibrium cooperative effect in the stepwise dissociation of the alpha subunits.
通过在含有0至137 mM异硫氰酸胍（GuSCN）的中性盐缓冲液中，将鼠伤寒沙门氏菌色氨酸合酶α2β2复合物离心至沉降平衡，研究了该复合物的解离平衡。在一个关于两个α亚基从稳定的β2亚基顺序解离的平衡模型的背景下，分析所得的浓度梯度。在这些实验条件下，仅在GuSCN浓度≤100 mM时可以评估第一个解离常数，仅在GuSCN = 137 mM时可以评估第二个解离常数。在中等GuSCN浓度下，两个解离常数都得到了足够明确的定义，以排除α亚基逐步解离过程中存在大的平衡协同效应。
