A study of angiotensin II binding sites in human placenta, chorion, and amnion

The binding of tritiated angiotensin II to 20,000 x g particulate tractions of human placenta, chorion, and amnion was investigated. Binding to particles from the three tissues reached equilibrium within 10 minutes at 29 degrees C and was displaced by the addition of 1,000-fold excess of unlabeled angiotensin II. Scatchard analysis of the data showed that two classes of binding sites were present in the placental preparation. For the high-affinity site, values of 9 x 10(-9) M and 300 fmoles/mg of protein were obtained for the dissociation constant and the binding capacity, respectively. There was little specific binding in chorion and amnion.