Incorporation of SP-40,40 into the solyble membrance attack complex(SMAC, SC5b-9) of complement

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Abstract
When SC5b-7 was prepared from the C8-depleted serum activated with inulin, it contained SP-40,40 as well as S-protein. From the densitometry of each component in SC5b-9 after SDS - PAGE, it was estimated that SC5b-9 was constituted of one molecule each of C5b, C6, C7, C8, S-protein, and SP-40,40 and two molecules of C9. SP-40,40 was depleted from normal serum with an affinity column using mouse monoclonal anti-SP-40,4O antibody. When the resulting SP-40,40-depleted serum was activated with inulin, SC5b-9 lacking SP-40,40 could be formed. S-Protein-depleted serum was also prepared with an affinity column using mouse monoclonal anti-S-protein antibody. Similarly, SC5b-9 lacking S-protein could be formed by the inulin activation of the S-protein-depleted serum. These results indicate that either SP-40,40 or S-protein should be able to form a soluble C5b-9 complex.