Effects of cations on affinity of calmodulin for calcium: ordered binding of calcium ions allows the specific activation of calmodulin-stimulated enzymes.
The acid stability of calmodulin has been used to devise a rapid and efficient method of decalcification based on trichloroacetic acid precipitation. Study of the competitive binding of K+, Mg2+, and Ca2+ to the Ca2+-binding sites of calmodulin has allowed determination of the intrinsic binding constants of each of the three cations for the four Ca2+-binding sites. The data are compatible with an ordered binding of Ca2+. If the Ca2+ sites are labeled A, B, C, and D starting at the NH2 terminus, the order of binding is postulated to be B, A, C, and D. The ordered binding properties support the suggestion that calmodulin translates quantitative Ca2+ signals into qualitatively different cellular responses.
D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000494:pharmacology*; D008433:Mathematics; D011188:Potassium / Q000494:pharmacology*
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D008274:Magnesium; D011188:Potassium; D002118:Calcium