Enthalpies of helix–coil transitions in polypeptides

✍ Scribed by F. E. Karasz; G. E. Gajnos

• Publisher: Wiley (John Wiley & Sons)
• Year: 1974
• Tongue: English
• Weight: 565 KB
• Volume: 13
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1974.360130407

✦ Synopsis

Abstract

Certain discrepancies in measured heats of helix–coil transitions in polypeptides are examined in terms of the theory of the effect of solvent composition on transition temperatures and heats in such systems. It is found, generally, that disagreement between enthalpy measurements conducted at fixed solvent compositions and isothermally may be expected because of the possibility of incomplete conversion of the polypeptide from the random‐coil to the helical conformations, or vice versa in one, or both, of these regimes in the course of the transition. The magnitude of the disagreement, if any, can depend quite critically on the particular region in the transition temperature–solvent composition plane in which measurements are undertaken. Application of these results to the system, poly‐γ‐benzyl‐L‐glutamate–dichloroacetic acid‐1,2‐dichloroethane, however, suggests that previously observed discrepancies in enthalpies here cannot be attributed to this phenomenon.