Complement inhibitor; binds C3 inhibiting proteolytic cleavage by C3 convertase (IC50 = 28 μM) and activation of classical and alternative complement pathways (IC50 values are 63 and 12 μM respectively). Prolongs graft survival and reduces hyperacute rejection of ex vivo pig kidneys perfused with human blood and inhibits in vivo heparin/protamine-induced complement activation in baboons.