Interaction between the third complement protein and cell surface macromolecules.

The activated form of the third complement protein, C3b, forms a stable complex with components of plasma membranes and particulate entities such as zymosan. The complex resists the action of detergents and protein denaturants as well as extremes of temperature, salt concentration, and pH. It can, however, be broken by exposure to hydroxylamine or by ammonolysis followed by incubation with sodium dodecyl sulfate. Thus, the complex appears to result from a hydrophobic interaction as well as a bond susceptible to nucleophilic attack.