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Studies on the conformation of protonated DNA
Author(s) -
Zimmer Ch.,
Luck G.,
Venner H.,
Frič J.
Publication year - 1968
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1968.360060410
Subject(s) - protonation , chemistry , cytosine , titration , dna , molecule , crystallography , nucleobase , stereochemistry , biochemistry , organic chemistry , ion
Experiments were made to demonstrate the predominant protonation effects and structural changes of the ordered double helical DNA structure and denatured state of DNA. Spectrophotometric titrations performed at different wavelengths indicate that cytosine can be protonated in the DNA double helical molecule to a high extent without breakdown of the secondary structure. With DNA heat‐denatured under severe conditions the protonation of cytosine can be measured at 280, 295, and 300 mμ: the apparent p K value obtained was ∼4.6. The protonated double helical conformation of the DNA molecule differs from the unprotonated state, which follows from the decrease of the thermal stability and from changes in the ORD curves. The ORD of a GC‐rich DNA indicates a novel Cotton effect with positive rotations at ∼260 mμ in 0.02 M KCl below pH 4.0 to pH 3.3. The occurrence of the new peak parallels the extent of protonated cytosine measured by the spectrophotometric titrations. It is concluded that the protonated cytosine in the double helical structure is responsible for the difference between the protonated DNA conformation and the native state at neutral pH.