Characterization and expression of c-type lysozyme cDNA from Japanese flounder (Paralichthys olivaceus).

Lysozyme is a widely distributed enzyme located in the serum, skin mucus, and other organs of fish, which is responsible for catalyzing the hydrolysis of the cell walls of most bacteria. A c-type of lysozyme cDNA was cloned from a kidney cDNA library of the Japanese flounder (Paralichthys olivaceus). The cDNAs consisted of 612 bp, which coded for 143 amino acid residues. The deduced amino acid sequence of Japanese flounder c-type lysozyme possessed 72.9%, 57.4%, and 65.4% identities with rainbow trout, chicken, and human c-type lysozymes, respectively. Comparison of the c-type lysozymes showed that the catalytic residues, the residues binding to sugar chains, and cysteine residues were completely conserved. Northern blot analysis indicated that the c-type lysozyme gene is apparently transcribed in the head kidney, posterior kidney, spleen, brain, and ovary of healthy flounder. When flounder were experimentally infected with Edwardsiella tarda, quantities of the c-type lysozyme mRNA increased in the head kidney, spleen, and ovary of the flounder.