Interaction between the labile binding site of human C4 and methylamine.

Human complement component C4 was irreversibly inactivated by low concentrations of methylamine at slightly alkaline pH. The inactivated C4 molecules lost the ability to bind to EAC1 cells but retained th capacity to participate in the formation of classical pathway C3 convertase in the fluid phase. 14C-methylamine was incorporated into the alpha-chain at a ratio of 1 mol methylamine per mol C4.