Ca2+-binding of S-100 protein in the presence of K+ and Mg2+.
Ca2+-binding of S-100 protein was studied using a Ca2+ electrode at pH 6.80. In the presence of 0.1 M KCl and 10 mM MgCl2 (ionic strength 0.13), Ca2+-binding to S-100 protein occurred in three steps with positive cooperativity. The numbers of bound Ca2+ ions in the three steps were 2, 2, and 4. The Ca2+-binding constants were 6.9 x 10(3) M-1, 2.9 x 10(3) M-1, and 3.7 x 10(2) M-1, respectively. The Ca2+-binding constants of the first and second steps obtained in the presence of 33.3 mM MgCl2 or 0.1 M KCl (ionic strength 0.10) were 1.4 times larger than those described above. This suggests that Mg2+ does not inhibit Ca2+-binding of S-100 protein. The increase of KCl concentration from 0.1 to 0.2 M caused a decrease of the Ca2+-binding constants to ca. 50%.
Matsuda
S
S
Hokkaido University of Education at Asahikawa.
D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology; D009418:S100 Proteins / Q000378:metabolism*
D009418:S100 Proteins; D008274:Magnesium; D011188:Potassium; D002118:Calcium