NMR observation of two states of triple helix in the thermal transition of (Pro-Pro-Gly)10

The thermal transition of (Pro-Pro-Gly)10 in D2O solution has been studied by NMR. The 1H and 13C spectra measured at different temperatures are assigned using homo- and heteronuclear two-dimensional NMR methods. It is confirmed that the triple helix undergoes a preliminary transition between two distinct states; the higher state is considered to be a preparatory state for the transition to the statistical coil. The observed change in the helix content is explained in terms of an extended first-order phase transition.