title: J chain in Rana catesbeiana high molecular weight Ig.
abstract: A polypeptide homologous to human and mouse J chain has been identified in the high molecular weight (HMW) Ig of the bullfrog, Rana catesbeiana. In previous studies, we had detected a component that was similar in size to mammalian J chains and that, relative to L chains, migrated rapidly to the anode in alkaline-urea PAGE; however, its mobility was less than that of mammalian J chains. We now demonstrate that this component is covalently linked to the H chain of R. catesbeiana HMW Ig. All of the disulfide bridges of this polypeptide, like those of human and mouse J chain, can be cleaved by reducing agents even in the absence of denaturing solvents. The putative frog J chain was isolated by a procedure that did not require preliminary purification of the HMW Ig. The chain differed in amino acid composition from L chains but resembled J chains from several other species. Tryptic peptides were isolated and sequenced. Except for a single heptapeptide, the peptides could be aligned by virtue of their similarity to segments of human and mouse J chain. Of the 116 residues that were placed, 55 were identical with residues in human J chain and 60 with residues in mouse J chain. The six cysteine residues identified in the frog J chain are at the same positions as six of the eight cysteines in the human and mouse J chains. The results indicate significant conservation in structure between amphibian and mammalian Ig J chains.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001704:Biopolymers; D004220:Disulfides; D006801:Humans; D007143:Immunoglobulin Heavy Chains; D007144:Immunoglobulin J-Chains / Q000302:isolation & purification*; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011489:Protein Denaturation; D011892:Rana catesbeiana / Q000276:immunology*
chemical_list: D000596:Amino Acids; D001704:Biopolymers; D004220:Disulfides; D007143:Immunoglobulin Heavy Chains; D007144:Immunoglobulin J-Chains; D046911:Macromolecular Substances