Isolation and partial characterization of immunoglobulin from a urodele amphibian (Necturus masculosus).

The primitive amphibian species, , a urodele, possessed serum immunoglobulin characterized by a mol. wt of approximately 900,000. Upon reduction of disulphide bonds and analysis under dissociating conditions, this molecule was resolved into polypeptide chains resembling light chains and μ-type heavy chains and having mol. wt of 22,000 and 70,000 respectively. The Necturus immunoglobulin was antigenically related to the IgM-like immunoglobulins of the toad () and the . Unlike these anuran amphibians, however, the Necturus did not possess detectable amounts of low molecular weight immunoglobulins. The finding raises the evolutionary possibility that the γ-like heavy chains of advanced amphibians may represent the results of a gene duplication independent of that which was responsible for the emergence of the γ heavy chain of mammals.