Isolation and preliminary characterization of two varieties of low molecular weight immunoglobulin in the bullfrog, Rana catesbeiana.

Two varieties of low m.w. immunoglobulins have been isolated from the serum of Rana catesbeiana frogs. They are highly cross-reactive, although each also contains unique antigenic determinants. Since both low m.w. immunoglobulins were identified in the serum of 22 individual frogs, it was concluded that they are isotypic variants. The light chains of R. catesbeiana and mammalian high and low m.w. immunoglobulins are similar in electrophoretic mobility on polyacrylamide gels containing sodium dodecyl sulfate. The heavy chains of fropg high m.w. immunoglobulins have the mobility of mammalian mu-chains; the heavy chains of both variants of frog low m.w. immunoglobulins migrate between mammalian mu- and gamma-chains in approximately the position of mammalian alpha-chains. An unusual structural feature of the R. catesbeiana high ald low m.w. immunoglobulins is that the unreduced proteins are partially dissociated in sodium dodecyl sulfate.