Ultrastructure of Secretory and High-Polymer Serum Immunoglobulin A of Human and Rabbit Origin
S- E. Svehag 1 and
B. Bloth 1
1 Department of Immunology, National Bacteriological Laboratory, S-105 21 Stockholm 1, Sweden
Electron micrographs of immunoglobulins A from human and rabbit colostrum, which were purified on tall agarose columns, revealed Y-shaped molecules (125 by 140 angstroms). The linear dimensions of the arms were 55 to 75 by 25 to 30 angstroms. A molecular model is postulated in which two immunoglobulin A monomers are superimposed on each other in a close-packed state with the secretory piece inserted in the constant region of the
-chains. High-polymer (11 or 13S) immunoglobulin A molecules (total span 100 to 110 angstroms) from human serum were composed of four arms (50 to 55 by 20 angstroms) joined at a contrast-rich center.