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Studies on the conformation of protonated DNA

✍ Scribed by Ch. Zimmer; G. Luck; H. Venner; J. Frič

Publisher
Wiley (John Wiley & Sons)
Year
1968
Tongue
English
Weight
598 KB
Volume
6
Category
Article
ISSN
0006-3525

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✦ Synopsis

Synopsis

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 a t 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 DKA heat-denatured under severe conditions the protonation of cytosine can be measured a t 280, 295, and 300 mp: the apparent pK value obtained was -4.6.

The protonated double helical conformation of the IINA molecule differs from the unprotonated state, which follows from the decrease of the thermal stability and from r.hanges in the ORD curves. The ORD of a GC-rich DNA indicates 3 novel Cotton efYect with positive rotations a t -260 mp in 0.02144 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 bet,ween the protonated DKA conformation and the native state a t neutral pH.

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