Fifth component of complement, which is cleaved by C5-convertase to form C5a, a 74-residue anaphylotoxin and potent chemotactic factor for leucocytes, and C5b. C5a rapidly loses a terminal arginine to form C5a desarg, which retains chemotactic but not anaphylotoxin activity. C5b combines with C6, C7, C8 and C9 to form a membranolytic complex.
Dictionary of molecular biology. 2004.