Tanokura M, Yamada K
FEBS Lett. 1985 Jun 3;185(1):165-9. doi: 10.1016/0014-5793(85)80763-8.
Microcalorimetric titrations of the two major isotypes of parvalbumin (PA1 and PA2) from bullfrog skeletal muscle with Ca2+ in the presence and absence of Mg2+ have been carried out at 25 degrees C and pH 7.0. The observed enthalpy titration curves were analyzed by the least-squares method. The measured enthalpy changes (delta H) of Ca2+ binding are -33.2 (PA1) and -16.3 kJ/mol site (PA2), and the entropy changes (delta S) are 28 (PA1) and 76 j/mol per K (PA2) in the absence of Mg2+. When 5 mM Mg2+ is present, the enthalpy change of PA2 (-26.7 kJ/mol) is about twice as large as that in the absence of Mg2+, whereas that of PA1 (-34.6 kJ/mol) is about the same. The entropy changes are 8 (PA1) and 29 J/mol per K (PA2). Both enthalpy and entropy changes are favorable for the Ca2+-binding reactions of PA1 and PA2 irrespective of the presence of Mg2+.
在25摄氏度和pH值为7.0的条件下，对牛蛙骨骼肌中两种主要亚型的小清蛋白（PA1和PA2），分别在有镁离子和无镁离子存在的情况下与钙离子进行了微量热滴定。通过最小二乘法对观察到的焓滴定曲线进行了分析。在没有镁离子的情况下，钙离子结合的测量焓变（ΔH）分别为-33.2（PA1）和-16.3 kJ/mol位点（PA2），熵变（ΔS）分别为28（PA1）和76 J/mol每K（PA2）。当存在5 mM镁离子时，PA2的焓变（-26.7 kJ/mol）约为无镁离子时的两倍，而PA1的焓变（-34.6 kJ/mol）大致相同。熵变分别为8（PA1）和29 J/mol每K（PA2）。无论是否存在镁离子，焓变和熵变都有利于PA1和PA2的钙离子结合反应。
