Open AccessEffect of Tightly Bound Divalent Cation on the Equilibria between G‐Actin‐Bound and Free ATP
Author(s) -
StrzeleckaGolaszewska Hanna
Publication year - 1973
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1973.tb03003.x
Subject(s) - divalent , chemistry , dissociation (chemistry) , actin , affinities , crystallography , biophysics , stereochemistry , biochemistry , organic chemistry , biology
The effects of various divalent cations on the rate of exchange of G‐actin‐bound ATP and on the rate of dissociation of ATP from G‐actin under conditions of a continuous removal of free ATP from the protein solution by Dowex‐1 were investigated. The order of inhibitory effects of equal concentrations of various cations on the ATP‐exchange rate did not parallel the order of affinities of the cations to the high affinity binding site in actin, inconsistent with what was expected on the basis of earlier findings. A kinetic analysis of the exchange of ATP in G‐actin preparations containing either Ca 2+ or Mg 2+ as the bound cation in the presence of various concentrations of the respective free cation revealed that the rate constants governing the equilibria between free and bound ATP in G‐actin solutions are markedly influenced by the kind of the G‐actin‐bound cation. The dependence of the rate of release of the bound ATP during incubation with Dowex‐1 on the kind of the bound cation (Ca 2+ , Mg 2+ or Mn 2+ ) led to the same conclusion. It is suggested that the conformation of the ATP binding site depends upon the cation bound at the high affinity site in actin.