Natural human C3a is prepared by cleavage of human C3 protein by a human C3 convertase. C3a is a member of the anaphylatoxin family of three proteins (C3a, C4a and C5a) produced by the activation of complement. It is an unglycosylated polypeptide containing 77 amino acids with a molecular mass of 9,089 daltons. Many of the biological functions of C3a are similar to those of C5a, but C3a is approximately 10- to 20-fold less active per microgram than C5a. C3a mediates many inflammatory responses including smooth muscle contraction, vasodilation, increased vascular permeability, and release of histamine from mast cells and basophils (Law, S.K.A. and Reid, K.B.M. (1995)). In contrast to C5a, C3a does not exhibit significant neutrophil stimulating activities and does not induce chemotaxis, granule release or superoxide production. C3a acts through the C3a Receptor (C3aR) which is a G-protein coupled receptor found widely distributed on peripheral tissues, lymphoid cells (neutrohphils, monocyes, and eosinophils) and in the central nervous system (astrocytes, neurons and glial cells) (Law, S.K.A. and Reid, K.B.M. (1995)). These activities of C3a are inactivated by removal of the C-terminal arginine and this occurs rapidly in plasma due to the action of carboxypeptidase N (Meuller-Ortiz, S.L., et al. (2009)).
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