CD spectra of isoionic DNA solutions

Area of Science:

• Biochemistry
• Molecular Biology
• Spectroscopy

Background:

• Deoxyribonucleic acid (DNA) exists in various structural forms depending on ionic conditions.
• Circular dichroism (CD) spectroscopy is a sensitive technique for probing DNA secondary structure and conformational changes.

Purpose of the Study:

• To investigate the ion-exchange transition of Na-DNA to H-DNA in salt-free solutions.
• To characterize the spectral changes associated with this transition using CD spectroscopy.
• To assess the reversibility of these structural changes.

Main Methods:

• Preparation of Na-DNA and H-DNA in concentrated salt-free solutions.
• Measurement of CD spectra across a relevant wavelength range (e.g., 200-300 nm).
• Ion-exchange chromatography for Na-DNA/H-DNA interconversion and spectral analysis.

Main Results:

• The Na-DNA to H-DNA transition induced substantial alterations in CD spectra.
• Significant decreases in the rotational force of negative bands at delta epsilon 249 (approx. 4-fold) and delta epsilon 279 (approx. 1.2-fold) were observed.
• The spectral changes were found to be largely irreversible, as evidenced by differences in spectra after neutralization or re-dissolution compared to the initial Na-DNA.

Conclusions:

• The ion-exchange transition significantly alters DNA conformation, impacting its spectral properties.
• The observed irreversibility suggests potential structural damage or stable conformational locking of H-DNA.
• Changes in CD spectra upon NaCl addition to isoionic DNA solutions indicate deprotonation and increased DNA hydration.