Conversion of ATP-actin to ADP-actin reverses the affinity of monomeric actin for Ca2+ vs Mg2+.
Monomeric ATP-actin binds Ca2+ 3-4-times more strongly than Mg2+ at pH 8. On conversion of G-ATP-actin to G-ADP-actin, the relative affinity of actin for the divalent cations is reversed, so that Mg2+ is bound 6-times more strongly than Ca2+. The dissociation rate constant of Ca2+ from Ca-ADP-actin is 50-fold higher than that for Ca2+ from Ca-ATP-actin, suggesting that this reversal of divalent cation affinities is due primarily to a higher equilibrium dissociation constant for Ca-ADP-actin. These results demonstrate an interaction between the actin-bound nucleotide and divalent cation or their binding sites.
D000199:Actins / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits
C042634:ADP-G-actin; C022920:ATP-G-actin; D000199:Actins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium