Chicken polymeric immunoglobulins of IgM from serum and IgA from bile and intestinal contents were purified and characterized for their subunit components. During the preparation of serum IgM by gel filtration on Sepharose 6B, two IgM with different m.w. were obtained. The major IgM (about 70% of the total IgM) had a m.w. of 860,000 and the minor IgM (about 30% of the total IgM) showed a smaller m.w. of 680,000, when determined by sodium dodecyl sulfate polyacrylamide (3%) gel electrophoresis (SDS-PAGE). It was assumed from the subunit analysis that the 860,000 IgM had a pentameric structure and that the 680,000 IgM might be tetrameric IgM. IgA purified from bile and intestinal contents, however, showed the same m.w. of 560,000 and was considered to have a trimeric structure. A homologue of J chain from chickens was identified in polymeric immunoglobulins of IgM and IgA but not in monomelic IgG by alkaline-urea-polyacrylamide gel electrophoresis, as well as by immunologic procedures and was purified from a completely reduced IgM by means of ion-exchange chromatography and gel filtration. Purified chicken J chain showed a m.w. similar to human J chain and it was calculated to be 19,000. The amino acid composition of chicken J chain was also determined and a striking similarity in the content of cysteine was found between J chain of chicken and mammals. However, marked differences in amino acid composition of chicken J chain were also observed in the contents of glutamic acid, asparatic acid, isoleucine, glycine, leucine, and phenylalanine, when compared with those of mammalian J chains. In spite of such differences in the amino acid composition between J chain of chickens and mammals, a precipitative cross-reaction between J chain of chickens and humans was observed with the antiserum to human J chain when reaction was allowed to proceed in agarose gel containing polyethylene glycol (Precipiplex). NH2-terminal amino acid could not be detected in the dansylated J chain, possibly indicating the blocked terminus similar to the human counterpart. A component that was different from the J chain in respect to its antigenicity and m.w. (around 30,000) but that had an electrophoretic mobility similar to J chain on alkaline-urea-PAGE was identified in the chicken IgM. It was associated with the IgM by disulfide linkage and could possibly be confused with the chicken J chain. Two kinds of light chains with different electrophoretic mobility on SDS-PAGE were identified in light chains from IgG, IgA, and IgM. Those two light chains were assumed to correspond to the two isotypes of light chains proposed recently by Leslie.
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Kobayashi et al. (1980) studied this question.