Extension Behavior of helicogenic polypeptides

The force laws governing the extension behavior of homopolypeptides are obtained from a phenomenological free energy capable of describing the helix-coil transition. Just above the melting temperature of the free chains, 7, the plot of force, f, vs end-to-end distance, R, exhibits two plateaus associated with coexistence of helical and coil domains. The lower plateau is due to tension induced onset of the helix-coil transition. The higher plateau corresponds to the melting of the helices by overextension. Just below T*, the fR plot exhibits only the upper plateau. The fR plots, the helical fraction, the number of domains and their polydispersity are calculated for two models. In one the helical domains are viewed as rigid rods while in the second they are treated as wormlike chains.