Comparison of immunoglobulin (IgM) from four fish species

Immunoglobulin (IgM) was isolated from the serum of four fish species, Atlantic salmon (Salmo salar L.), halibut (Hippoglossus hippoglossus L.), haddock (Melanogrammus aeglefinus L.) and cod (Gadus morhua L.) and a comparison made of some physical and biochemical properties. The molecular weight of IgM varied between the different species and between the different analytical methods used. IgM from all four species was tetrameric in serum although a proportion of the molecule was held together by noncovalent forces. Salmon and haddock IgM were composed of two IgM types as regards the overall charge whereas halibut and cod IgM were homogeneous in this respect. The molecular weight of the heavy and light chains was similar for all four species. The oligosaccharide moiety, which was N-linked and associated with the heavy chain varied from 7.8 to 11.4% of the total molecular weight. Lectin analysis indicated variable composition of the carbohydrate moiety between species. The sensitivity to PNGase and trypsin varied between the four species.