Isolation of placental-type alkaline phosphatase associated with human syncytiotrophoblast membranes using monoclonal antibodies.

Placental-type alkaline phosphatase (PLAP) has been purified from human term syncytiotrophoblast microvillous plasma membranes by immunoaffinity chromatography using the immobilized monoclonal antibodies H317 and H315. The eluted enzymatically active PLAP had a molecular weight in the regions of 115K and 130K, with an occasional higher molecular weight form at 180K. On reduction to a 66K monomeric form, both enzymatic activity and immunoactivity against the PLAP-reactive monoclonal antibodies were lost. The monomeric form of syncytiotrophoblast microvillous plasma membrane- (StMPM-)associated PLAP displayed electrophoretic polymorphism on 2D-PAGE.