Native human C3 is a naturally glycosylated polypeptide containing two disulfide-linked chains. C3 is central to the activation of all three pathways of complement activation. Initiation of each pathway generates proteolytic enzyme complexes (C3 convertases) which are bound to the target surface. These enzymes cleave a peptide bond in C3 releasing the anaphylatoxin C3a and activating C3b. For a brief time (~60 us) this nascent C3b is capable of reacting with and covalently coupling to hydroxyl groups on the target surface. Description: Human serum/plasma. Synonyms: C3 protein.