Ultraviolet difference spectroscopy of intermediates trapped in unfolding and refolding of bovine pancreatic trypsin inhibitor.
The solvent surface accessibilities of the aromatic amino acids of bovine pancreatic trypsin inhibitor have been examined after the protein has been trapped at various stages of unfolding and refolding. Two types of near-ultraviolet difference spectroscopy were used in making these measurements. One type compares the near-ultraviolet spectrum of each protein with the spectrum of the native inhibitor; the other is solvent perturbation spectroscopy. The two types of difference spectroscopy utilized are compared and found to be equivalent measures of tyrosine solvent exposure if the perturbation spectra are corrected for a probable contribution by buried residues. The experimental values for tyrosine solvent exposure in the native inhibitor are in agreement with those calculated from its crystal structure. The results of these studies identify an order in which the four tyrosines and the four phenylalanines of bovine pancreatic trypsin inhibitor are removed from solvent as refolding proceeds. The relative solvent accessibilities of the aromatic residues suggest an ordering in which the protein chain obtains compact globular structures.
D000818:Animals; D002417:Cattle; D003553:Cystine / Q000032:analysis; D005026:Ethylene Glycols / Q000494:pharmacology; D008958:Models, Molecular; D010179:Pancreas / Q000201:enzymology; D010649:Phenylalanine / Q000032:analysis; D011487:Protein Conformation; D011489:Protein Denaturation; D013056:Spectrophotometry, Ultraviolet; D014361:Trypsin Inhibitors / Q000032:analysis*; D014443:Tyrosine / Q000032:analysis
D005026:Ethylene Glycols; D014361:Trypsin Inhibitors; D014443:Tyrosine; D010649:Phenylalanine; D003553:Cystine