Isolation of lysozyme and an antifungal peptide from sea lamprey (Petromyzon marinus) plasma

The sea lamprey (Petromyzon marinus) belongs to the most primitive class of fish and has only innate immunity. The innate immune factors, lysozyme and an antifungal peptide, were isolated from sea lamprey plasma. Sea lamprey plasma (40.1 mg protein/ml) was assayed for lysozyme activity by gel diffusion assay. Using hen egg white lysozyme standards, plasma concentration of lamprey lysozyme was 5 μg lysozyme/mg total protein. The presence of lysozyme in such high concentration in lamprey plasma could be important in their innate immunity and resistance to infection. Lysozyme and the antifungal peptide were isolated by low molecular weight gel filtration chromatography from sea lamprey plasma. Gel filtration chromatography yielded two peak tubes containing lysozyme (1 μg/211 μg total protein) and antifungal peptide (1 μg/66 μg total protein). Lysozyme and antifungal activity of each fraction were determined by well diffusion assay using Gram-negative bacteria, Gram-positive bacteria and two fungal species. The molecular weight of lamprey lysozyme was 14.3 kDa. The sea lamprey lysozyme was effective against Gram-positive bacteria but not against Gram-negative bacteria or fungi. Molecular weight of the antifungal peptide was approximately 3000 Da. Antifungal plasma activity was seen against Penicillium notatum and Aspergillus flavus. No plasma antibacterial peptide was found.