Erickson Jeffrey R, Sidell Bruce D, Moerland Timothy S
Department of Biological Science, Florida State University, Tallahassee, FL 32306-4370, USA.
Comp Biochem Physiol A Mol Integr Physiol. 2005 Feb;140(2):179-85. doi: 10.1016/j.cbpb.2004.12.001. Epub 2005 Jan 11.
Parvalbumin (PV) is a soluble calcium-binding protein that is especially abundant in fast-twitch muscles of fish and other lower vertebrates. Despite its prevalence in ectothermic taxa, few data address the effects of temperature on PV binding function. In this study, calcium dissociation constants (KD) were measured as a function of temperature (0-25 degrees C) for PV from two Antarctic (Gobionotothen gibberifrons and Chaenocephalus aceratus) and two temperate zone fish species (Cyprinus carpio and Micropterus salmoides). Measurements by fluorometric competitive binding assay show that KD values for PVs from the Antarctic species were significantly higher at all assay temperatures and were less sensitive to temperature relative to carp and bass. However, estimates of KD are fundamentally similar for PVs from the Antarctic and temperate zone species when examined at their native physiological temperature. Variation in pH and ionic strength within a physiologically relevant range had only modest effects on KD. Thermodynamics of calcium binding to PV from G. gibberifrons and C. carpio was measured by isothermal microcalorimetry. When measured at 15 degrees C, the Gibbs free energy change (deltaG) was significantly greater for calcium binding to PV from G. gibberifrons than from carp (-43.4+/-1.5 kJ mol(-1) and -46.6+/-3.0 kJ mol(-1), respectively), and the relative contribution of entropy to deltaG for calcium binding to PV from the Antarctic species was about twice that of carp (deltaS=16.0+/-0.8 J degrees C(-1) mol(-1) for G. gibberifrons; deltaS=7.5+/-0.8 J degrees C(-1) mol(-1) for C. carpio).
小清蛋白（PV）是一种可溶性钙结合蛋白，在鱼类和其他低等脊椎动物的快肌中含量尤其丰富。尽管它在变温动物类群中普遍存在，但很少有数据涉及温度对PV结合功能的影响。在本研究中，测量了来自两种南极鱼类（裸盖鱼和南极头带冰鱼）和两种温带鱼类（鲤鱼和大口黑鲈）的PV的钙解离常数（KD）随温度（0-25摄氏度）的变化情况。通过荧光竞争结合测定法测量表明，在所有测定温度下，南极物种的PV的KD值均显著更高，并且相对于鲤鱼和鲈鱼，其对温度的敏感性更低。然而，当在其原生生理温度下进行检测时，南极和温带物种的PV的KD估计值基本相似。在生理相关范围内，pH值和离子强度的变化对KD的影响较小。通过等温微量热法测量了钙与裸盖鱼和鲤鱼的PV结合的热力学性质。在15摄氏度下测量时，钙与裸盖鱼的PV结合的吉布斯自由能变化（ΔG）显著大于与鲤鱼结合的情况（分别为-43.4±1.5 kJ·mol⁻¹和-46.6±3.0 kJ·mol⁻¹），并且对于来自南极物种的PV，熵对钙结合的ΔG的相对贡献约为鲤鱼的两倍（裸盖鱼的ΔS = 16.0±0.8 J·°C⁻¹·mol⁻¹；鲤鱼的ΔS = 7.5±0.8 J·°C⁻¹·mol⁻¹）。
