[52-Homoserine]-basic pancreatic trypsin inhibitor. Preparation and properties of a protein analog.

Treatment of basic pancreatic trypsin inhibitor (BPTI) with cyanogen bromide smoothly cleaves the polypeptide chain at the single methionyl residue. The newly formed homoserine lactone and alpha-amino functions are held in proximity by a disulfide linkage, and in neutral aqueous solution react together spontaneously to re-form the peptide chain. The resulting analog, [52-homoserine]-BPTI is very similar to the native molecule in most properties measured. The rate of formation of this analog from the chain-cleaved intermediate has been determined. It is apparent that the facility of analog synthesis is due in large part to the retention of the native protein conformation in the cyanogen bromide-cleaved intermediate.