Effect of Fluoro-Amino Acids on Protein Secondary Structure Stability Richard Cheng, Department of Chemistry, University at Buffalo, SUNY Buffalo, NY 14260-3000 The stability of enzymes catalysts for application in organic synthesis can be improved by incorporating fluorinated amino acids. We aim to measure the -helix and -sheet propensities of fluoro-amino acids. This would be useful for quantitatively predicting the effect of fluoro-amino acids on protein stability. We have measured the helix propensity (in both monomeric helices and dimeric coiled coils of fluoro-amino acids such as Hfl, showing that helix propensity decreases significantly upon introducing fluorines. We have also measured the sheet propensity of fluoro-amino acids such as Hfl, showing that sheet propensity increases upon introducing fluorines. This suggests that fluoro-amino acids such as Hfl may be more suitable for stabilizing -sheet structures compared to -helices to realize the full potential of the fluoro-stabilization effect.