Distinctive subpopulations of catfish serum antibody and immunoglobulin

High molecular weight antibodies and immunoglobulin of the channel catfish were found to be composed of heterogeneous mixtures of covalent subpopulations. Although these proteins appeared tetrameric in physiological buffers (mol. wt approximately 700,000), molecular weight estimates in the presence of the detergent sodium dodecyl sulfate indicated that they dissociated into eight distinct subpopulations. Each dissociative subpopulation was found to be stable under the conditions of electrophoretic analysis, and furthermore each was apparently composed of equimolar H and L chains. Based upon relative mobilities it seems probable that the catfish antibody was composed of various combinations of covalent linkages between covalently-linked H-L chain pairs, i.e. 8, 7, 6, 5, 4, 3, 2 and 1. Further studies suggest the presence of size heterogeneity in catfish light chains. Whether or not this distinction represents isotypic L chain differences is not yet known but these findings coupled with the complex architecture of the physiological tetramer suggest an unusual and previously unappreciated level of complexity present in fish antibody.