Ultrastructure of Human C1q Protein

THE first component (C1) in the complement system may be defined functionally as a macromolecule capable of binding to antigen-antibody complexes and inducing the sequential reactions of this system. C1 consists of three distinct proteins named C1q, C1r and C1s which,in serum, form a macromolecular complex held together by calcium ions¹. The C1q protein was first isolated by Müller-Eberhard and Kunkel² and Taranta et al.³. The ultrastructure of this basic, heat-labile 11S protein is outlined here.