J-chain-like component in 18-S immunoglobulin of the skate Raja kenojei, a cartilaginous fish.

A J-chain was found in the IgM, an 18-S pentameric immunoglobulin, of the skate, Raja kenojei, a cartilaginous fish, by means of gel filtration-column chromatography of reduced and radioalkylated immunoglobulin, followed by alkaline-urea polyacrylamide gel electrophoresis. The J-chain showed an electrophoretic mobility equivalent to that of the light chain, and much slower than that of the J-chain in human IgM. Its electrophoretic banding patterns, however, were different from those of the light chain. Its mol. wt of 17,500 was close to that of mammalian J-chain. The J-chain was not found in another immunoglobulin of the skate, a 9-S dimer held by a noncovalent force. No immunological cross-reactivity was observed between the skate J-chain and human and chicken J-chains. In view of these findings, it was concluded that the J-chain in the skate IgM is both electrophoretically and antigenically considerably different from the J-chain in mammalian IgM.