A 19-residue antimicrobial peptide parasin I is generated from histone H2A in the skin mucus of catfish by the action of cathepsin D activated by a procathepsin D-processing enzyme induced upon epidermal injury. Here we report the isolation and characterization of the procathepsin D-processing enzyme in the mucus of wounded catfish. Sequence analysis of the cDNA identified the purified procathepsin D-processing enzyme as matrix metalloproteinase 2 (MMP 2). By acting as a procathepsin D convertase upon epidermal injury, MMP 2 is involved in the regulation of parasin I production in catfish skin mucosa. (C) 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.