Isolation and Characterization of Fig Lysozyme

A procedure is described for the isolation of fig lysozyme from dried fig latex. The pure enzyme has a molecular weight of 29,000 and consists of a single polypeptide chain with amino-terminal glycine and carboxyl-terminal isoleucine residues. With Micrococcus lysodeikticus cells as substrate, the enzyme exhibits a sharp pH optimum at pH 4.5. Fig lysozyme is considerably more active toward chitin and tetra-N-acetyl-d-glucosamine than egg-white lysozyme. The enzyme shows a strong ionic strength dependence, maximal activity being attained at an ionic strength of 0.02 to 0.03. The physical and enzymatic properties of fig lysozyme are strikingly similar to those of papaya lysozyme, although the amino acid compositions of the two enzymes show many differences. Fig lysozyme, just as papaya and egg-white lysozymes, is powerfully inhibited by histamine. A mechanism for this inhibition is suggested.