Pyrrolidonecarboxylic Acid at the N-Terminal Positions of Polypeptide Chains from Leopard Shark Immunoglobulins

Abstract

Abstract Leopard shark immunoglobulins are found in 7S and 17S forms, which are indistinguishable chemically and antigenically, and probably are analogous to IgM molecules of mammals (1). The two molecular forms thus appear to share common H and L polypeptide chains. Suran and Papermaster reported that the amino terminal 6 residues from H- and L-chains of at least a portion of 7S and 17S leopard shark Ig were virtually identical to each other and to the homologous regions of kappa L-chains of mouse and man (2). These results suggest that relatively little divergent evolution had occurred in this region of H- and L-chains at the level of the elasmobranchs and support the common origin of these chains by duplication of an ancestral gene (3, 4). However, lambda L-chains and the gamma and mu H-chains from mammalian Ig almost invariably possess a blocked N-terminal residue identified as pyrrolidonecarboxylic acid (PCA).