Tanokura M, Imaizumi M, Yamada K
FEBS Lett. 1986 Dec 1;209(1):77-82. doi: 10.1016/0014-5793(86)81087-0.
Microcalorimetric titrations of the major isotype of parvalbumin (tPA) from toad (Bufo) skeletal muscle, with Ca2+ in the presence and absence of Mg2+ and with Mg2+ in the absence of Ca2+, have been carried out at 25 degrees C and pH 7.0. The results indicate that the two binding sites in each molecule are distinguishable from each other for both Ca2+ binding and Mg2+ binding. Such a characteristic is distinctly different from those of other parvalbumins. The enthalpy changes determined are distinctly different from those of bullfrog parvalbumins on Ca2+ or Mg2+ binding, but are similar to those on Mg2+-Ca2+ exchange. The results indicate that the reaction of Mg2+-Ca2+ exchange is driven almost entirely by the large favorable enthalpy change.
在25℃和pH 7.0条件下，对蟾蜍（Bufo）骨骼肌中主要同型肌钙蛋白（tPA）进行了微量热滴定，滴定过程中存在和不存在Mg2+时加入Ca2+，以及不存在Ca2+时加入Mg2+。结果表明，每个分子中的两个结合位点在结合Ca2+和Mg2+时彼此可区分。这种特性与其他肌钙蛋白明显不同。所测定的焓变与牛蛙肌钙蛋白结合Ca2+或Mg2+时的焓变明显不同，但与Mg2+-Ca2+交换时的焓变相似。结果表明，Mg2+-Ca2+交换反应几乎完全由巨大的有利焓变驱动。
