Aggregation of DNA enhanced by the protoberberine alkaloids, coralyne and berberine

The aggregation of DNA caused by coralyne was studied by spectroscopic, viscosity and electric birefringence measurements. Aggregation was markedly enhanced over a narrow range of coralyne to DNA phosphate ratio and then followed by precipitation. The electric birefringence measurements indicated that the ratio at the maximal aggregation varied depending on the concentration of coralyne, finally reaching 1:1 at higher concentrations. The particles (type I) for such enhanced aggregation were estimated to be prolate ellipsoids 1700-4000 A in length with a diameter of 1400-4000 A. At higher coralyne concentrations, another particle (type II) was formed which was a thick rod-like particle 1700-4000 A in length with a diameter of 120-210 A. These dimensions indicate that type I and II particles consist respectively of several tens of thousands and some hundreds of molecules of DNA. On the other hand, berberine did not produce such a marked aggregation of DNA, and the result was a thick rod-like particle 1700-4000 A in length with a diameter of 300-1000 A. The enhancement by coralyne and berberine is discussed in terms of intermolecular interactions.