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Description

Native, human C3b complement component. Cleavage of the C3-alpha chain at peptide bond 77 by either of the complement C3 convertase enzymes results in production of C3a (M.W. 9083) and C3b (M.W. 180,000) fragments. The C3b fragment is a glycoprotein composed of the modified C3-alpha chain (alpha') (M.W. 105,000) and the intact C3-beta chain (M.W. 75,000). Nascent C3b has the transient ability to form a covalent ester bond with a variety of target surfaces. Once bound to target surfaces C3b becomes an essential subunit of both the classical and alternative pathway C5 cleaving enzymes. In addition, surface-bound C3b has opsonic and immune adherence activities which are mediated via binding to CR1 (CD35) complement receptors.