[The cation selectivity of calcium-binding structures of skeletal muscle. A physico-chemical interpretation as an...

The binding forces acting in the binding of Ca and certain multivalent cations (Ce3+, La3+, Mg2+, Sr2+, Ba2+) in the membrane system fo skeletal muscles are discussed. From the similarity of effects in these biological binding sites and cation-exchange resins has been concluded an identity of both binding mechanism. The exchange affinity in the skeletal muscle decreases in the following order: Ce3+ greater than La3+ greater than Mg2+ greater than Sr2+ greater than Ba2+. This sequence of selectivity is in contrast to the sequence which should be expected in view of the ionic diameters. On the other hand, the same selectivity reversal can be seen in phosphonous and phosphonic cations-exchange resins. Because of that we conclude the binding of Ca and other multivalent cations in membrane system of skeletal muscle to be a point-shaped, polar adsorption--predominantly at phosphate groups. Possibly these groups hold a special selectivity (specifity) related to strongly hydrated and polarizable cations.