Specific and reversible interaction between pregnancy-associated plasma protein A and heparin.

An interaction between heparin and circulating pregnancy-associated plasma protein A (PAPP-A) has been observed. This interaction could be reversed by the addition of the specific heparin antagonist protamine sulphate. In the presence of heparin, crossed immunoelectrophoretic analysis revealed an alteration in the electrophoretic mobility of PAPP-A, while a significant increase (22 to 64 per cent, P less than 0.02) in measured levels of PAPP-A was seen in electroimmunoassays. These findings are discussed in relation to the optimal conditions for the precise measurement of PAPP-A.