Enzymatic hydrolysis of hen egg lysozyme and separation of antimicrobial peptides

The objectives of this project were the isolation, purification, and characterization of the antimicrobial peptides from chicken egg white lysozyme hydrolysate obtained by treatment with pepsin followed by trypsin. This hydrolysate, composed of over 20 small peptides, had no enzymatic activity but was still active against Gram-positive bacteria (Staphylococcus aureus 23-394) and Gram-negative bacteria (Escherichia coli K-12, ATCC 10798). The bactericidal peptides were purified and sequenced. One peptide with the sequence Ile-Val-Ser-Asp-Gly-Asp-Gly-Met-Asn-Ala-Trp, inhibited Gram-negative bacteria Escherichia coli K-12 and corresponded to residue 98-108 which is located in the middle part of helix-loop-helix. Another novel antimicrobial peptide inhibited Staphylococcus aureus 23-394 and also characterized to have the sequence His-Gly-LeuAsp-Asn-Tyr-Arg-Gly, corresponding to residue 15--22 of lysozyme. These peptides broadened lysozyme bactericidal activity to Gram-negative bacteria. They may open up new opportunities for lysozyme applications as natural antimicrobial agents in food preservation and also for therapeutic purposes.