DNA binding studies of magnesium(II), calcium(II), barium(II) and ATP complexes

We have investigated the ways by which magnesium(II), calcium(II) and barium(II) and their ATP complexes bind to B-DNA. Effects on native calf thymus DNA conformation were studied and compared with those involving the uncomplexed metal ions and the polymer. It was found that MgATP(-2), CaATP(-2) and BaATP(-2), interact with the phosphates of the polynucleotide; only BaATP(-2) appears to bind also through the bases. ATP complexes cause transitions mainly to the B family. The C form is induced by small amounts of MgATP(-2) or CaATP(-2). At high complex concentrations (r = 2.5 or 5) the polynucleotide adopts the psi(-) conformation, while BaATP(-2) induces this transition at r = 0.6. A contribution of the A form is observed in the case of CaATP-DNA at r = 0.6 and at the beginning of the reaction in the Ba-DNA system at 22 degrees C, for r = 5. The alkaline earth metal ions induce a stabilization of the B conformation. Structural changes with magnesium(II) at r = 2.5 are interpreted in terms of a B to C transition. Calcium(II) at r = 5 produces the A form. In other cases the alkaline earth metal ions stabilize the B conformation. It was found that they all interact with the phosphates of the polynucleotide. The binding ratio, r, is an important factor in an structural changes.