CHARACTERIZATION OF LOW-SALT AND HIGH-SALT CONFORMATION OF POLY(DI-DC) BY HYDROGEN-DEUTERIUM EXCHANGE KINETICS - A CLASSICAL RAMAN-SPECTROSCOPY STUDY

Poly(dI-dC) in H2O and D2O solution can undergo different equilibrium geometries which strongly depend on the salt nature and concentration. These structures were studied by classical Raman spectroscopy in orde r to monitor a hydrogen-deuterium exchange kinetics in 8-CH group in i nosine. Spectral and isotopic exchange rate changes depending on NaCl concentration were observed and interpreted on the basis of previously obtained results from resonance and classical Raman spectroscopy stud ies of poly(dI-dC) and hydrogen-deuterium exchange measurements of dif ferent conformations of nucleic acids. It is shown that: i) the Raman spectrum of low-salt poly(dI-dC) corresponds to the right-handed polym er with characteristic bands for B conformation, but the value of the retardation factor of isotopic exchange suggests that this form is not a pure canonical B form and that it contains some portion of the A fo rm, ii) the Raman spectrum of the high-salt poly(dI-dC) corresponds to the right-handed polymer with characteristic bands for both the A and B conformations, iii) the retardation factor of hydrogen deuterium ex change for the high-salt form of poly(dI-dC) is essentially higher tha n in the low-salt form which indicates a dominant presence of the A fo rm in the high-salt conformation of poly(dI-dC). This leads to the con clusion that the high-salt conformation of poly(dI-dC) is a mixture of A and B forms with the predominant A form.