Equilibrium dialysis study of binding of hexammine cobalt(III) to DNA

In recent years there has been great interest in using hexammine cobalt(II1) as an isovalent analogue of spermidine.Hexammine cobalt(II1) qualitatively mimics spermidine in many of its physical effects on nucleic acids.Quantitatively, however, there are often large differences in the effects of the two ions.Both spermidine and hexammine cobalt(II1) promote the collapse of various DNAs into compact structures.'-4Up to 5 times the amount of spermidine, compared to hexammine cobalt(III), is required to cause collapse.The B-Z transition can be driven by either ion.The transition, driven by hexammine cobalt(II1) binding, is observed in d(pCpG), ,5 poly(dG-dC), ' and poly(dG-m5dC).' Poly(dG-dC) also undergoes a B-Z-