BENNETT
e t al.
Phylogeny of Immunoglobulins. Characterization of a 14s Immunoglobulin from the Gar, Lepisosteus osseus* Ronald T. Acton,i Peter F. Weinheimer,$ Harry K. Dupree, E. Edward Evans, and J. Claude Bennett5
The immune macroglobulin from the longnose gar, Lepisosteus osseus, has been purified and physicochemically characterized. The macroglobulin was found to have a sedimentation coefficient of 13.9 S and a molecular weight of 610,000. There was a total of 4.97% carbohydrate with a residue distribution different from human macroglobins. The molecule was found to contain 82 disulfide bonds and dissociation into heavy (H) and light (L) chains could be observed following total reduction and alkylation in 7 M guanidine hydrochloride. The H and L chains could be separated by gel filtration and were found to have molecular weights of ABSTRACT:
I
mmunoglobulin M (IgM) in mammals has been characterized as having a molecular weight of approximately 900,000 and is composed of five disulfide-bonded subunits, each of which consists of two heavy ( p ) and two light ( K or A) chains (Miller and Metzger, 1965; Lamm and Small, 1966; Putnam et a/., 1967; Bennett, 1969). The polypeptide chains were shown to have molecular weights of 66,000-75,000 for the H chain and 23,000 for the L chain. This pentameric structure of IgM suggested by physical and chemical studies has been confirmed by ultrastructural studies (Chesebro et a/., 1968; Feinstein and Munn, 1969; Shelton and Mclntire, 1970) and serves to distinguish it from other mammalian immunoglobulin classes. Limited physicochemical data suggest that birds, reptiles, amphibia, and elasmobranchs possess immunoglobulins resembling mammalian IgM (Marchalonis and Edelman, 1966; Clem and Small, 1967; Leslie and Clem, 1969; Acton et al., 1970a; Saluk et a/., 1970). The need for understanding structural and functional relationships and the genetic mechanisms of immunoglobulin synthesis warrants further study from the standpoint of the phylogeny of these molecules. The object of this investigation was to isolate and characterize the IgM-like molecules from a primitive bony fish,
* From the Department of Microbiology and the Division of Clinical Immunology and Rheumatology, Department of Medicine of the University of Alabama in Birmingham, The Medical Center, Birmingham, Alabama, and the Southeastern Fish Cultural Research Laboratory, Marion, Alabama. Receiced Airgirsr 28, 1970. This in\sestigation \+:is supported by grants from the United Statcs Public Health Ser\ice (AI-02693, AI-91 53, AM-03555), the National Science Foundation (Grant GB-5983), and the John A . Hartford Foundation. A preliminary report of this work \\as presented before the Federation of American Societies for Experimental Biology in April 1970, at Atlantic City, PI'. J. Postdoctoral Rcsearch Fello~vsupported by U. S . Public Health Scr\ ice Training Grant 5-T0l-00293. $ Postdoctoral Research Fellow supported by U. S. Health Service Kcsearch Fellowship lFOZAM42874-01A 1 , 8 Recipiait of a Research Carcer Development award (1
