title: Interaction of divalent cations with human red cell cytoskeletons.
abstract: The binding of Ca2+ to spectrin from human erythrocytes was investigated by equilibrium dialysis, and the binding of Mn2+ by electron paramagnetic resonance. The results led to the conclusion that no binding sites of high affinity (greater than about 10(4) M-1) are present. In the cytoskeletal protein complex isolated from erythrocytes, which (like crude spectrin) contains actin and some other proteins, a set of sites with an association constant of 4 x 10(4) M-1 for Mn2+ is observed. These may be divalent cation binding sites on the actin molecules. Weak interactions of Ca2+ and Mg2+ with spectrin are reflected by self-association of the spectrin heterodimers, which can be followed in the analytical ultracentrifuge and by light-scattering. This self-association is affected by the state of the protein thiol groups. Conditions in which self-association of spectrin occurs have been defined. No aggregation is observed at the Mg2+ activity thought to correspond to that in the cytoplasm.
mesh_terms: D000042:Absorption; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D004910:Erythrocyte Membrane / Q000378:metabolism*; D004912:Erythrocytes / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism; D008345:Manganese / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D013049:Spectrin / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D013049:Spectrin; D008345:Manganese; D008274:Magnesium; D002118:Calcium