PHYSICOCHEMICAL CHARACTERIZATION OF C3B RECEPTORS ISOLATED FROM HUMAN-ERYTHROCYTES BY IMMUNOPRECIPITATION

  • 1 January 1980
    • journal article
    • research article
    • Vol. 41  (4) , 929-936
Abstract
A high yield of active C3b [complement component 3b] receptors was obtained by solubilizing human erythrocyte membranes with 2 M K Br, whereas other solubilization agents yielded no, or significantly less activity. Gel filtration of the K Br lysates revealed that the apparent MW of biologically active C3b receptor molecules was greater than 106. Immunoprecipitates prepared with radio-iodinated K Br lysates and anti-C3 receptor sera (AC3RS) were subjected to sodium dodecyl sulfhate polyacrylamide gel electrophoresis (SDS-PAGE) or sodium dodecyl gel filtration. Unreduced SDS-PAGE and gel filtration profiles showed 3 predominant peaks with apparent MW of 1 1.3 .times. 106, 80,000 and 60,000. Whereas the high MW component decreased only slightly after reduction, the 80,000 and 60,000 MW components disappeared and 2 new peaks with apparent MW of 38,000 and 18,000 appeared in SDS-PAGE profiles. Although the high MW component present in reduced SDS-PAGE profiles was detectable in some control experiments, none of the other peaks could be precipitated with control sera, and these components were demonstrated only when KBr lysates of C3b receptor-positive erythrocytes and AC3RS that were able to inhibit C3b receptor ligand binding were used for precipitation. Apparently the C3b receptors of human erythrocytes in its biologically active state is a macromolecule with an apparent MW higher than 106 and the protein moiety consists predominantly of noncovalently linked protein molecules with apparent MW of 80,000 and 60,000. These protein molecules are composed of disulfhide-bridged polypeptide chains with apparent MW of 38,000 and 18,000.