肌球蛋白与二磷酸腺苷相互作用的量热研究。

Calorimetric studies of the interaction of myosin with ADP.

作者信息

Kodama T, Woledge R C

出版信息

J Biol Chem. 1976 Dec 10;251(23):7499-503.

Abstract

A calorimetric titration method was used to study ADP binding to native myosin. Data were analyzed by assuming that the myosin molecule has n independent and identical sites for ADP binding. The enthalpy change (deltaH), the binding constant (K), and n were determined. In 0.5 M KCl, 0.01 M MgCl2, and 0.02 M Tris/HCl (pH 7.8), we found: at 0 degrees, deltaH = -57.1 +/- 3.2 kJ-mol-1, log K = 6.42 +/- 0.13, n = 1.49 +/- 0.07; at 12 degrees, deltaH = 73.1 +/- 3.2 kJ-mole-1, log K = 6.08 +/- 0.13, and n = 1.74 +/- 0.07. The average heat capacity change on ADP binding to myosin between 0 and 12 degrees is thus -1.4 +/- 0.4 kJ-mol-1-K-1. Reasonably consistent results were obtained at 25 degrees, suggesting ADP binding to myosin is as strongly exothermic as at lower temperatures, although further interpretation of this result seems unwarranted, mainly because of the instability of myosic at this temperature. The number of protons released on binding of ADP to myosin was determined in separate experiments. The value was 0.19 +/- 0.02 at both 0 and 12 degrees. The reaction of protons with Tris thus contributes about -9.5 kJ-mol-1 to the observed heat on ADP binding.

摘要

采用量热滴定法研究了ADP与天然肌球蛋白的结合。通过假设肌球蛋白分子具有n个独立且相同的ADP结合位点来分析数据。测定了焓变（ΔH）、结合常数（K）和n。在0.5 M KCl、0.01 M MgCl₂和0.02 M Tris/HCl（pH 7.8）条件下，我们发现：在0℃时，ΔH = -57.1±3.2 kJ·mol⁻¹，log K = 6.42±0.13，n = 1.49±0.07；在12℃时，ΔH = -73.1±3.2 kJ·mol⁻¹，log K = 6.08±0.13，n = 1.74±0.07。因此，0至12℃之间ADP与肌球蛋白结合时的平均热容变化为-1.4±0.4 kJ·mol⁻¹·K⁻¹。在25℃时获得了合理一致的结果，表明ADP与肌球蛋白的结合与较低温度下一样强烈放热，不过对此结果进一步解读似乎没有必要，主要是因为肌球蛋白在该温度下不稳定。在单独的实验中测定了ADP与肌球蛋白结合时释放的质子数。在0℃和12℃时该值均为0.19±0.02。质子与Tris的反应因此对ADP结合时观察到的热量贡献约为-9.5 kJ·mol⁻¹。