Chemical and Immunological Properties and Amino Acid Sequences of Three Lysozymes from Peking-Duck Egg White

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Abstract
Three lysozymes (DLs-1, -2, and -3) were purified from Peking-duck egg white by adsorption on CM-Sephadex C-25 resin, followed by CM-Sephadex C-25 and Sephadex G-50 column chromatographies. The three enzymes each moved as a single band, but showed different electrophoretic mobilities, on disc-polyacrylamide gel electrophoresis at pH4.1. Final yields of DL-I, DL-2, and DL-3 were 18.2%, 22.0%, and 6.0%, respectively, from the crude material adsorbed on CM-Sephadex resin. The enzymatic activities of DL-1, DL-2, and DL-3 were 1.53, 1.52, and 1.34 times that of hen egg white lysozyme, respectively, using Micrococcus lysodeikticus cell wall as a substrate at pH 6.2 and 37°C. All the DLs lacked histidine and their amino acid compositions differed from each other by a few amino acid exchanges. The amino acid sequences of DL-2 and DL-3 differed from that of DL-1 by two displacements (Ser-37 to Gly and Gly-71 to Arg) and three displacements (Pro-79 to Arg in addition to the same substitutions), respectively. In comparison with Duck II and Duck III lysozymes from Kaki-duck (Hermann and Jollès (1970) Biochim. Biophys. Ada200 , 178–179; Hermann et al . (1971) Eur. J. Biochem . 24 , 12–17) as regards amino acid sequences, Duck II is identical to DL-1 except for one displacement of Gln-57 in DL-1 to Glu in Duck II, while Duck III is rather different from our three lysozymes. All DLs gave single precipitin lines with any rabbit antisera against DLs and each precipitin line fused completely with that of any of the DLs in Ouchterlony double diffusion tests. However, the radiobinding inhibition assay showed that some anti-DL antisera clearly discriminated fine differences among the three DLs. The displacement at residue 79 (Pro↔Arg) gave the clearest immunological difference among the three kinds of displacements found in DLs.