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Studies on the Subunit Structure of Rabbit Secretory IgA^1,2,

From the Division of Clinical Immunology, Sunnybrook Hospital, The Institute of Immunology, and the Departments of Medicine and Medical Cell Biology, University of Toronto, Toronto, Ontario, Canada

Abstract

The nature of the intersubunit bonds in rabbit secretory IgA dimer was investigated by employing gel filtration on 2% and 4% agarose columns equilibrated with 6 M guanidine-HCl. Under these conditions, rabbit secretory IgA behaved as a dimer [(H₂L₂)₂] which established that the bonds linking the monomer subunits were covalent in nature. Rabbit secretory component, however, dissociated from the native molecule in 6 M guanidine-HCl, which indicated that the secretory component was bound to the native dimer by non-covalent bonds. Mild reduction and alkylation with dithiothreitol (DTT) in aqueous buffer resulted in dissociation of the rabbit secretory IgA dimer molecule to monomer subunits and lower molecular weight material. Reduction with varying quantities of DTT showed that rabbit secretory IgA dimer was more resistant to reduction than human secretory IgA dimer which in turn was more resistant to reduction than a human IgA dimer myeloma protein.

Footnotes

¹ Address reprint requests to: Brian J. Underdown, Ph.D., Division of Clinical Immunology, Sunnybrook Hospital, 2075 Bayview Avenue, Toronto 12, Ontario, Canada.

² Supported by the Medical Research Council of Canada (Grant MA 4050).