Figure 4. Perturbation of duplex stability of the DNA target by osmolytes.
A, Salt-dependence (0.15, 0.375, and 1 M NaCl) of the helix-coil transition as measured by UV thermal melting. B, Effect of EG, betaine, maltose, and urea on DNA duplex stability in the presence of 0.375 M NaCl. Samples containing osmolytes were 1.2 osmolal in total osmolality. The molal concentrations of the osmolytes were 0.52 m (EG), 0.53 m (betaine), 0.45 m (maltose), and 0.63 m (urea). The green curve is without osmolyte. C, DSC thermograms of DNA melting in the presence of 0.69 m nicotinamide and 0.375 M NaCl, corresponding to 1.2 total osmolal. D, Summary of the effects of osmolytes on thermal stability of 1.4 μM duplex DNA. The Tm in nicotinamide was back-extrapolated to 1.4 μM duplex via Tm−1 vs. the logarithm of duplex concentration.