title: Does DNA acid fixation produce left-handed Z structure?
abstract: The effects of acetic acid (HCOOCH3) on the solution structure of calf-thymus DNA are studied at pH 7.3-2.5 with acid/DNA(P) (phosphate) molar ratios (r) of 1/40, 1/20, 1/10, 1, 2, 10, 20 and 40. Fourier Transform infrared (FTIR) difference spectroscopy is used to establish correlations between spectral changes and base protonation, DNA conformational transition and structural variations of the acid-DNA complexes in aqueous solution. The FTIR difference spectroscopic results showed that protonation of cytosine and subsequent unpairing of the G-C base pairs begins at pH 4-3 and continues up to pH 2.5, where a complete base separation and base unstacking occur. Similarly, protonation of A-T base pairs starts at pH 4-3 and is completed at pH 2.5, where base separation and base unstacking are observed. The protonation of the G-C base pair leads to the formation of Hoogsteen-type H-bonding, before a complete G-C disruption. The biopolymer protonation leads to the formation of several non-B-DNA structures, including left-handed Z conformation.
authors.affiliation: Centre de recherche en photobiophysique, Université du Québec à Trois-Rivère, Canada.
authors.forename: H A
authors.initials: HA
authors.lastname: Tajmir-Riahi
authors.forename: J F
authors.initials: JF
authors.lastname: Neault
authors.forename: M
authors.initials: M
authors.lastname: Naoui
mesh_terms: D000818:Animals; D001482:Base Composition; D002417:Cattle; D004247:DNA / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009690:Nucleic Acid Conformation; D017550:Spectroscopy, Fourier Transform Infrared; D013950:Thymus Gland
chemical_list: D004247:DNA