title: A calorimetric study of Ca2+ binding by the parvalbumin of the toad (Bufo): distinguishable binding sites in the molecule.
abstract: 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.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002023:Bufo bufo; D002118:Calcium / Q000378:metabolism*; D002151:Calorimetry; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D010320:Parvalbumins / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D009124:Muscle Proteins; D010320:Parvalbumins; D008274:Magnesium; D002118:Calcium