Differential scanning calorimetry studies of the inverse temperature transition of the polypentapeptide of elastin and its analogues

Differential scanning calorimetry studies have been carried out on the sequential polypeptide of elastin, (L‐Val¹–L‐Pro²–Gly³–L‐Val⁴–Gly⁵)_n, abrreviated as PPP, and its more hydrophobic analogues (L‐Val¹–L‐Pro²–Gly³–L‐Val⁴–Gly⁵)_n, referred to as Leu¹‐PPP, and (L‐Ile¹–L‐Pro²–Gly³–L‐Val⁴–Gly⁵)_n, referred to as Ile¹‐PPP. Consistent with inverse temperature transitions, the temperatures of the transitions for which maximum heat absorption occurs are inversely proportional to the hydrophobicities of the polypentapeptides (31°C for PPP, 16°C for Leu¹‐PPP, and 12°C for Ile¹‐PPP), and the endothermic heats of the transitions are small and increase with increasing hydrophobicity, i.e., 1.2, 2.9, and 3.0 kcal/mol pentamer for PPP, Leu¹‐PPP, and Ile¹‐PPP, respectively. Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order, as the temperature is raised above that of the transition, has been repeatedly observed using different physical characterizations. Furthermore, the studies demonstrated indentical conformations for PPP and Ile¹‐PPP above and below the transition. Both heats and temperature of the transitions vary with hydrophobicity, but not in simple proportionality.