Purification and characterization of two lysozymes from rainbow trout (Salmo gairdneri)

1. Two different lysozymes, designated I and II, were purified from the kidney of rainbow trout. The enzymes had isoelectric points of approximately 9.5 and 9.65, and differed in their binding characteristics to a cation exchanger. Lysozyme II had the highest specific activity against Micrococcus luteus. 2. By sodium dodecyl sulphate gel electrophoresis, a molecular mass of 14.4 kDa was established for the two lysozymes. 3. For both type I and II enzymes, optimum pH under the present conditions was 5.5 and optimum temperature (at pH 6.2) around 45 degrees C. 4. N-terminal amino acid sequence determination indicated that the two trout lysozymes were c-type lysozymes. 5. The fish lysozymes had a much higher rate of diffusion in agar than did the other lysozymes tested (possibly due to less interaction with agarose). This implies that a foreign lysozyme, such as hen egg white lysozyme, should not be used as a standard when assaying lysozyme activity with the lysoplate technique.