The temperature dependence and thermodynamic functions of partitioning of substance P peptides in dodecylphosphocholine micelles

Abstract

The temperature dependence of the partition of a neuropeptide, Substance P (SP), and its [Tyr8] analogue in a widely used membrane mimic, dodecylphosphocholine micelles, was studied by using a pulsed field gradient nmr diffusion technique. The partition coefficient was found to decrease when the temperature is increased, indicating a favorable (negative) enthalpy change upon partitioning of the peptides. Thermodynamic functions of the partitioning were determined. The enthalpy of partition ΔHpart, was found to be in the −2.5 to −3.0 kcal/mol range, which is between 2 and 3 times higher than the entropic term −TΔSpart. The free energy of partitioning is consistent with a model in which the SP peptides interact with the micelles mainly through the hydrophobic side chains of the residues Phe7, Phe8 (or Tyr8), Leu10, and Met11, and without the insertion of a major portion of the peptide into the hydrophobic core of the micelles. © 1998 John Wiley & Sons, Inc. Biopoly 45: 395–403, 1998