Complement: substitution of the terminal component in immune hemolysis by 1,10-phenanthroline.

The participation of metal ions in the terminal step of immune cytolysis was investigated with chelating agents. 1,10-Phenanthroline induced lysis of sensitized sheep erythrocytes which had reacted with the first eight components of human complement. Hemolysis caused by 1,10-phenanthroline resembled lysis produced by the ninth component of complement in dependence on cell-bound eighth component and on temperature and in inhibition by 0.09M ethylenediaminetetraacetic acid. Bivalent metal ions reduced the hemolytic capacity of 1,10-phenanthroline, and Fe(++) inhibited the activity of the ninth component. Since trivalent iron had no such effects, it is postulated that the hemolytic activity of 1,10-phenanthroline and the ninth component of complement is a function of their affinity for Fe(++).