Parasin I is a 19-amino acid histone H2A-derived peptide isolated from the skin of the catfish, and shows antimicrobial activity. In Vitro: Parasin I with comparable antimicrobial activities localized to the cell membrane and subsequently permeabilized the outer and cytoplasmic membranes. Parasin I and its active analogs show strong cytoplasmic membrane permeabilizing activity^[1]. Codon optimized parasin I fused with human lysozyme is expressed in Pichia pastoris, and has potent antibiotic activity^[2].