Effect of glycine on DNA structural transitions induced by multivalent cationic compounds

We have investigated the effect of glycine (an organic osmolyte) on several DNA transitions induced by Tb3+, spermidine3+ and spermine4+ addition, using light scattering, circular dichroism, UV spectroscopy and electric linear dichroism techniques. DNA condensation and B-Z transition by the three compounds is perturbed by glycine: more Tb3+, spermidine3+ and spermine4+ must be added to obtain the same extent of condensation or Z-form as compared to the behaviour in the absence of this organic osmolyte. However, according to the light scattering experiments, glycine has also a structural effect on the DNA condensation that could be explained by an influence of the medium dielectric constant on the morphology of particles formed or on the rate of the condensation process. Contrary to these transitions, the particular B-B'-psi transition resulting from the addition of Tb3+ to a DNA solution is not observed in the presence of glycine. Since the chelation of Tb3+ by the phosphate group and the N-7 of guanine is presumably responsible for this transition, the glycine effect could probably be explained by a perturbation of this chelation by the change in solvent polarity and the chelating ability of the organic osmolyte.