Temperature sensitivity of calcium binding for parvalbumins from Antarctic and temperate zone teleost fishes

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 °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 °C, the Gibbs free energy change (ΔG) 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 ΔG for calcium binding to PV from the Antarctic species was about twice that of carp (ΔS=16.0±0.8 J °C−1 mol−1 for G. gibberifrons; ΔS=7.5±0.8 J °C−1 mol−1 for C. carpio).