An alkene isostere of Gly-trans-Pro was synthesized and incorporated into a host Ac-(Gly-Pro-Hyp)(8)-Gly-GlyTyr-NH2 peptide to investigate the effect of locking a proline amide bond. Proline amide bond isomerization is the slow step in collagen folding. By locking the amide, we hypothesized an increase in stability of the collagen triple helix. The substitution instead destabilized the collagen host peptide. The T-m value of the host control peptide was 50.0 degrees C, while the peptide containing the isostere,Ac-(Gly-Pro-Hyp)(3)-Gly-psi[(E)CH=C]-Pro-Hyp-(Gly-Pro-HyP)(4)-G ly-Gly-Tyr-NH2, had a T-m value of 28.3 degrees C. There are clearly factors that contribute to Collagen stability and folding that we do not yet understand.