The α- and β-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 α-chain was PAS positive whereas the β-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 α subunit. Reconstitution of C5 from its isolated chains, followed by trypsinization resulted in slightly less activity than that from the individual α subunit. These findings provide direct support for previous evidence suggesting the biologic activity for neutrophils derives entirely from the α subunit of C5. This represents the first report of direct recovery of biologic activity from a purified subunit chain of C5.

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This work was supported by United States Public Health Service Grants AI 09651 and HL 07202.

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