α-Helix formation by solvent–solvent interaction

✍ Scribed by Noah Lotan; Mordechai Bixon; Arieh Berger

• Publisher: Wiley (John Wiley & Sons)
• Year: 1967
• Tongue: English
• Weight: 426 KB
• Volume: 5
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1967.360050108

✦ Synopsis

The degree of helicity 0 of a series of homologous polypeptides as a function of solvent composition was investigated. The polypeptides studied were: poly-N6-(3-hydroxy-propy1)-cglutamine (PHPG) as well as the corresponding 2-hydroxyethyl and 4hydoxybutyl derivatives (PHEG and PHBG, respectively). PHPG, which is nonhelical in formic acid, attains helicity on addition of relatively small amounts of formates, formamide, and nrea t,o its solntion in formic acid. This demonstrates that the high acidity of pure formic acid is largely responsible for its helix-breaking power-probably through protonation of the peptide bonds. In formic acid-water mixtures all three polymers show a maximum in degree of helicity a t a mole fraction of about 0.3 formic acid. This is interpreted as being due to interaction between the two helix-breaking solvents, which resnlts in the formation of an inactive molecular species. It is shown that solventinduced transitions with helicitly maxima are predicted by the Rixon-Lifson treatment when applied to this syst,em.