The sequence of events involved in haemagglutination and lysis of erythrocytes by washed cells, vesicles and the culture supernate of strain W83 was monitored by Cr release and transmission electronmicroscopy. All preparations, except capsular material and lipopolysaccharide, caused haemagglutination and, by a slow process of attachment and specific attack on the surface structures of the red blood cells, produced minute pores and eventual leakage of cellular contents. N-acetylglucosamine, N-acetylgalactosamine and several other sugars such as glucose and sucrose had no effect on haemagglutination. Antiserum raised against a cloned haemagglutinin of strain 381 inhibited the activity of strain W83 cells, vesicles and supernate. The antiserum-neutralised supernate lost 70–80% of its hydrolytic activity towards α-N-benzoyl-L-arginine-4-nitroanilide but the residual activity behaved in a manner similar to the native supernate in that it was completely inhibited by the addition of 2,2′-dipyridyl disulphide and was fully restored upon addition of a low-M mercaptan. Binding of the antiserum to the haemagglutinin epitope of still permitted titration of the active centre cysteinyl thiol group of the proteinase. Purified gingivain caused lysis of erythrocytes and was not neutralised by antiserum to the haemagglutinin. These results suggest that, although the haemagglutinin and gingivain are probably separate molecules, they are closely associated on the outer membrane of and may be functionally related.


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