Changes in the c.d. spectra of calf thymus DNA induced by sequential polypeptides in trifluoroethanol solutions. Part II

Interactions between calf thymus DNA and ( -Arg-X-Gly)_n sequential polypeptides (where

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) in trifluoroethanol: water (40:60) solutions in the salt range of 0.12—0.5 NaCl, were studied using c.d. spectroscopy. It was found that DNA tertiary structure (ψ form) is modulated by the nature of the polypeptides (variation of X residue). The effect of the secondary structure of polypeptides on the formation of ψ-DNA was also analysed. Unordered polypeptides destabilized ψ aggregates, while helical polypeptides favoured DNA tertiary structure. A loss of tertiary structure was observed in the presence of the ( -Arg- -Val-Gly)_n, which can be attributed to the ability of valine to suppress ψ-type DNA.