Immunoblotting analysis of the peptide chain structure of the physiological breakdown products of the third component of human complement

Immunoblotting after sodium dodecyl sulfate polyacrylamide gel electrophoresis of the purified third component of human complement (C3) and its fragments and of unpurified C3 and its degradation fragments in serum or plasma has been examined. The pattern of C3 degradation observed corresponded well with previous observations made with purified proteins. The immunoblotting technique demonstrated a high resolution, and proved to be capable of providing a full analysis of mixtures of C3 fragments in serum with the use of chain‐fragment‐specific antibody preparations. Additional heterogeneity in C3 and its breakdown products were observed, and covalent adducts between activated C3 and other proteins were detected directly in serum and plasma without any purification of the components. The results further indicated that antibodies raised against denatured C3 reacted quantitatively and qualitatively better with the nitrocellulose‐bound C3 than those antibodies raised to native C3, probably reflecting the paratially denatured state of molecules after separation by polyacrylamide gel electrophoresis and blotting onto the nitrocellulose.