Isolation and characterization of two membrane-associated placental tissue proteins

Two membrane associated placental tissue proteins (PP4 and MP1) have been isolated and characterized. Both proteins are found in the soluble as well as solubilized protein fractions of the human placenta and thus appear to be at least partly associated with placental membranes. PP4 has a molecular weight of 35000 and apparently consists of a single peptide chain. It has an electrophoretic mobility in between the alpha 1- and alpha 2-globulins, an isoelectric point of 4.85 and a sedimentation coefficient of 3.3 S. The carbohydrate content of PP4 amounts to 2.4%. MP1 was isolated from placental protein fractions solubilized with Triton X-100. It has a molecular weight of around 18000 and appears to be composed of two identical subunits which are non-covalently linked. MP1 was found to have an electrophoretic mobility in between the alpha 2- and beta 1-globulins, an isoelectric point of 4.75 and a sedimentation coefficient of 6.65 S. MP1 is a glycoprotein which contains 9.6% carbohydrates. Immunochemical methods were used to detect and quantitate PP4 and MP1 in extracts of placentae and other human tissues. MP1 appears to be specific to the placenta, whereas PP4 was found to occur also in certain other human tissues. The diagnostic significance of detection and measurement of these proteins in tissues and body fluids is presently under investigation.