Melanostatin conformations in solution

✍ Scribed by Robert W. Schwartz; Wayne L. Mattice; Morris A. Spirtes

• Publisher: Wiley (John Wiley & Sons)
• Year: 1979
• Tongue: English
• Weight: 772 KB
• Volume: 18
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1979.360180802

✦ Synopsis

Abstract

The conformations of melanostatin have been studied experimentally using CD spectroscopy and via calculations. In aqueous solution and 2,2,2‐trifluoroethanol (TFE) there is no evidence that monomers of the tripeptide exist in an ordered (β‐bend) structure. In water and TFE solutions (3–6 × 10^−4^M) the neutral molecules aggregate very slowly, taking about 3 days to attain equilibrium at room temperature. At equivalent concentrations in TFE, although not in water, the cationic molecules also slowly aggregate, although to a lesser extent. Calculations using rotational isomeric state theory give the most probable unperturbed end‐to‐end distance of the molecule at 9.3 ± 0.1 Å and indicate that a vast majority of the molecules exist in some extended conformation, end‐to‐end distance ≥6 Å. Only 0.4% of the molecules are calculated to have O…︁H separations compatible with a β‐bend structure. An intramolecular hydrogen bond must have an energy at least 2 kcal/mol lower than that of an intermolecular hydrogen bond to solvent if a β‐bend is to be experimentally observable.