title: Kinetic studies of calcium binding to parvalbumins from bullfrog skeletal muscle.
abstract: In addition to steady-state properties of calcium binding to parvalbumins, kinetic studies are required for adequate evaluation of the physiological roles of parvalbumins. By using a dual-wavelength spectrophotometer equipped with a stopped-flow accessory, the transient kinetics of calcium binding to parvalbumins (PA-1 and 2) from bullfrog skeletal muscle was examined at 20 degrees C in medium containing 20 mM MOPS-KOH, pH 6.80, 0.13 mM tetramethylmurexide, 25 microM CaCl2, metal-deprived PA-1 or PA-2, various concentrations of Mg2+, and KCl to adjust the ionic strength of the medium to 0.106. The results can be explained in terms of the following rate constants under the conditions mentioned above when a second-order kinetic scheme is assumed. For PA-1, the association and apparent dissociation rate constants for Ca2+ are 1.5 X 10(7) M-1 X s-1 and 1.5 s-1, respectively, or more. The rate constants for Mg2+ are 7,500 M-1 X s-1 and 5-6 s-1, respectively. For PA-2, the rate constants for Ca2+ are 7 X 10(6) M-1 X s-1 and 1.16 s-1, respectively, and those for Mg2+ are 3,500 M-1 X s-1 and 3.5-4 s-1, respectively. Increased affinities for Ca2+ and Mg2+ at 10 degrees C are largely due to decreased apparent dissociation rate constants for these divalent cations, because no significant change in the association rate constants was found.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D007700:Kinetics; D008433:Mathematics; D008956:Models, Chemical; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D010320:Parvalbumins / Q000378:metabolism*; D011485:Protein Binding; D011892:Rana catesbeiana; D014336:Troponin / Q000378:metabolism; D019209:Troponin C
chemical_list: D002147:Calmodulin; D009124:Muscle Proteins; D010320:Parvalbumins; D014336:Troponin; D019209:Troponin C; D002118:Calcium