Abstract
Equilibrium dialysis studies and sedimentation experiments with soluble rat liver chromatin and radioactive 45Ca support the hypothesis that there is a specific binding of Ca2+ to chromatin molecules. At low ionic strength the binding constant is about 12 l/mM indicating that more than half of the negative charges of the chromatin molecules are neutralized due to the binding of Ca2+ at appropriate concentrations. This effect possibly accounts for low concentration of Ca2+ and other divalent cations being effective in inducing compact higher order structures of chromatin. Monovalent cations are not specifically bound, but high concentrations cause unspecific shielding of the charges on the chromatin molecules and thus structural transformation. Even under these high salt conditions a specific binding of Ca2+ to chromatin occurs. The binding constant is, however, only 0.4 l/mM due to the lower effective concentration of the charged chromatin molecules which is reduced by unspecific neutralizing.
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