Determination of the Disulfide Array in Sapecin, an Antibacterial Peptide of Sarcophaga peregrina (Flesh Fly)1

Sapecin is a 40-residue peptide containing 6 half-cystine residues. The disulfide structure of sapecin was determined by sequencing cystine-containing peptides obtained by digesting sapecin with thermolysin. Results showed that sapecin has a vortical structure fixed by 3 disulfide bonds between cysteine residues 3 and 30, 16 and 36, and 20 and 38, respectively, and that these disulfide bonds are essential for its antibacterial activity.