Expression of Japanese flounder c-type lysozyme cDNA in insect cells

Lysozyme is a widely distributed hydrolase which likely plays an important role in bio-defense systems. In the current study, we constructed a baculov irus expression system for the c-type lysozyme cDNA of Japanese flounder (P aralichthys olivaceus) and evaluated the activity of the recombinant protei n. This activity was estimated, by turbidimetric assay, to be 7.7 U/mg, a v alue five times higher than that of hen egg white (HEW) c-type lysozyme exa mined under the same conditions. The optimum pH and temperature for the lyt ic activity of the Japanese flounder c-type recombinant lysozyme were found to be 5.0-6.5 and 40 degreesC, respectively. Two groupings for fish lysozy me activity are proposed: the first has an optimum pH of approximately 6.0 and the second an optimum pH of above 8.0. Flounder c-type lysozyme was fou nd to possess little lytic activities against Edwardsiella tarda and Strept ococcus sp. This latter characteristic may help explain the fact that these two bacterial species are responsible for significant disease problems in cultured Japanese flounder. (C) 2001 Published by Elsevier Science Ltd.