Generation of biologic activity from the purified alpha-chain of C5

The alpha- and beta-chains of the fifth component of human complement (C5) have been isolated and their physical and biologic properties have been characterized. After electrophoresis in SDS-poly-acrylamide slab gels, the chains were eluted from the gels and extensively dialyzed. The amino acid composition of each chain was then determined. On SDS-gels, the alpha-chain was PAS positive whereas the beta-chain revealed little or no staining. As a measure of chemotactic activity, the lysosomal enzyme-releasing activity of both chains was examined before and after trypsinization; activity resided almost entirely in the alpha subunit. Reconstitution of C5 from its isolated chains, followed by trypsinization resulted in slightly less activity than that from the individual alpha subunit. These findings provide direct support for previous evidence suggesting the biologic activity for neutrophils derives entirely from the alpha subunit of C5. This represents the first report of direct recovery of biologic activity from a purified subunit chain of C5.