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From the Research Laboratories of the Department of Pediatrics and Pathology, University of Minnesota Hospitals, University of Minnesota, Minneapolis, Minnesota 55455
Abstract
The subunit nature of bowfin (Amia calva) immunoglobulins was examined by a variety of physicochemical techniques. Dithiothreitol (DTT) reduced the 13.6S bowfin immunoglobulin, thought to be tetrameric, into monomeric subunits. The limited reduction procedure, designed to reduce only inter-subunit disulfides, cleaved light chains from the subunits and resulted in loss of the parent molecule's ability to agglutinate Brucella abortus. Relatively weak non-covalent bonding was detected between the heavy and light chains of both the high and low molecular weight bowfin immunoglobulins. The isolated bowfin heavy and light chains possessed CD spectra not unlike those of human µ heavy chains and 
light chains examined under identical solvent conditions. A mass difference, not attributable to carbohydrate, of 
12,000 was detected between the heavy chains of the two size classes of bowfin immunoglobulin. When the heavy chains were compared antigenically, no differences were detected. Mass deletions of this nature lent support to the hypothesis that immunoglobulins evolved by end-to-end duplication of a primordial gene coding for approximately 110 amino acids.
Footnotes
1 This work was aided by grants from the National Science Foundation, The National Foundation-March of Dimes, United States Public Health Service (AI-00292, AI-08677, AI-00798), the American Cancer Society, and the Graduate School, University of Minnesota.
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