Studies on the inhibition of C56-initiated lysis (reactive lysis). III. Characterization of the inhibitory activity C567-INH and its mode of action.

An activity in serum which inhibits reactive lysis has recently been shown to do so by preventing the attachment of C567 complexes to cells, and hence has been designated C567-INH. This report describes certain physiochemical characteristics of the inhibitory activity. It behaves as a heat-stable pseudoglobulin, soluble in 20 per cent Na2SO4, and having alpha1 mobility on Pevikon block electrophoresis. It is excluded from CM cellulose at pH 6-0, RSC Equals 0.007 M, is retained by an XM-100 membrane and is heterogenous on Sephadex G-200, eluting in at least two peaks. The combined active materials from the Sephadex column elute from DE-52 in at least four peaks. The mechanism of action of material from each of these four peaks is shown to involve prevention of attachment of C567 complexes to membranes, and this is shown to involve an effect on C567 complexes in solution rather than an effect on the membrane. A less dramatic effect on the lysis of EC567 by limited quanities of C8 and C9 can be demonstrated. Haemolytic studies using cell-bound C567 suggest that the interaction of C567-INH with C567 involves a loose reversible association. It is therefore postulated that C567-INH inhibits reactive lysis primarily by reversibly associating with the nascent C567 complex in solution, increasing its bulk and decreasing its diffusion capacity so that it is unable to reach a cell membrane before its haemolytic potential decays.