ABSTRACT
Table 1 ACTIVATORS OF THE ALTERNATIVE PATHWAY OF HUMAN COMPLEMENT
Table 2 PROTEINS OF THE ALTERNATIVE PATHWAY
C3b expresses binding sites for Factors B, H, I, P, C5, and C3b receptors, none of which are present on native C3. A conformational change, which can be detected spectrophotometrically, probably accounts for the appearance of these function^.^^-^^ This conformational change can be induced without peptide bond cleavage by any reaction that severs the thioester bond as illustrated in Figure 1. Hydrolysis of the thioester produces C3(H20) which is conformationally and functionally C3b-like except that it lacks an attachment It is thought that C3(H20) formed by spontaneous hydrolysis in plasma initiates the pathway as will be described below. '
