Binding of specific peroxidase-labeled antibody to placental-type phosphatase on tumor-derived membrane fragments.

Monospecific antiserum to human placental alkaline phosphatase was purified by immunoabsorption and labeled with horseradish peroxidase. The binding of this labeled antibody to membrane fragments prepared from placental and tumor tissue was measured using agarose gel filtration to separate bound antibody. The antibody bound only to membrane fragments which contained placental phosphatase, and the amount bound varied in the order ascitic fluid membrane fragments greater than tumor extracts greater than placental extracts. Absorption of the antibody with crude placental membrane yielded a population of antibody which reacted with tumor tissue and pure placental enzyme, but only slightly with placental membranes. These results are interpreted to suggest that some antigenic sites are exposed in tumor tissue membranes which are not in placental membranes.