BINDING STOICHIOMETRY OF GADOLINIUM TO ACTIN - ITS EFFECT ON THE ACTIN-BOUND DIVALENT-CATION

Using 45Ca2+ and 153Gd3+ we studied the effects of binding the lanthanide ion, gadolinium, to skeletal muscle G-actin. Gd3+ can specifically displace 6-7 Ca2+ from their binding sites on actin. Furthermore, a total of 6-7 Gd3+ can be shown to bind to actin, and this result is not affected by the subsequent addition of polymerizing quantities of KCl. We conclude that Gd3+ binds only to the Ca2+-binding sites of actin. The number of these Gd3+ sites closely corresponds to the known number of high and low affinity sites for divalent cations such as Ca2+. © 1979.