Isolation and characterization of immunoglobulin-like proteins of the Australian lungfish (Neoceratodus forsteri).

Abstract

SummaryProteins resembling immunoglobulins of other vertebrate species in physical and chemical properties were instigated from the serum of unimmunized Australian lungfish (Neoceratodus forsteri). Two types of antigenically related proteins, characterized by sedimentation coefficients of 19.4S and 5.9S, were observed. Both proteins possessed light polypeptide chains which resembled typical immunoglobulin light chains in molecular weight (23,000) and behaviour in gel electrophoresis. The 19.4S proteins were similar to γM immunoglobulins of other vertebrates in size and chain structure. Heavy polypeptide chains from these molecules were comparable to the μ‐chain in molecular weight (70,000) and gel electrophoretic properties. The heavy chain of the 5.9S immunoglobulin‐like protein differed from those of the major classes of vertebrates in possessing a molecular weight of approximately 40,000. In both proteins the light chains and heavy chains were linked through disulfide bonds.These data suggest that lungfish resemble higher vertebrates in possessing different immunoglobulin classes defined by the presence of distinct heavy chains. The low molecular weight type of immunoglobulin‐like proteins may represent a class of immunoglobulins which is unique to Dipnoi.