Complex dielectric constant of arginine-DNA and protamine-DNA aqueous systems at 10 GHz

The complex dielectric constant of arginine and protamine from herring sperm (clupeine) and their complexes with herring sperm DNA was measured at 10 GHz in the temperature range -20 to +45 degrees C by a microwave cavity perturbation method. The experimental results were analysed in terms of a three-component equation (solute molecules, interfacial water and bulk water) to calculate the fractional volume of modified water and hence the specific hydration of the samples. A fourfold reduction of the specific hydration is observed for the clupeine molecule as compared to the free monomers. This is consistent with a folded conformation of the protein in solution. The specific hydration of the complex between clupeine and DNA is reduced by 50% with respect to the weighted average for the uncomplexed components. This result indicates an intimate contact between clupeine and DNA with exclusion of water molecules and is consistent with the highly condensed form of nucleoprotamines which is known in vivo.