Mutagenesis of Bovine Pancreatic Trypsin Inhibitor (BPTI) To Examine the Effects of Individual Amino Acid Replacements to Proline in Protein Stability Citlalin Xochime, Mandie Jensen, and David P. Goldenberg. Biochemistry Dept., University of UtahUtah, SLC, UT 84112 Mutant forms of bovine pancreatic trypsin inhibitor (BPTI) containing an amino acid replacement to proline are being developed for use in further studies of protein stability and the BPTI folding mechanism. Further studies are important in comparing the folding kinetics of mutant BPTI with wild-type BPTI. Mutants that alter the folding mechanism will identify sites along the polypeptide backbone where conformational constraints are important for the folding process. Activity was observed for BPTI variants with a residue replacement of Ile 19 to Pro (I19P), Ala 25 to Pro (A25P), or Thr 32 to Pro (T32P), indicating that these substitutions are tolerated by the folded protein. Other BPTI variants with a residue replacement of Gly 28 to Pro, Gln 31 to Pro, or Asn 44 to Pro are in varying stages of development.