Purification and characterization of two new soluble placental tissue proteins (PP13 and PP17)

Two new soluble placental tissue proteins (PP13 and PP17) have been isolated and characterized. PP13 has an electrophoretic mobility the same as that of albumin, an isoelectric point in the range 4.7-4.8 and a sedimentation coefficient of 3.1 S. Its molecular weight was found to be 30 000. PP13 appears to be composed of two identical subunits which are held together by disulfide bonds. PP17 has an electrophoretic mobility in between the beta 1- and alpha 2-globulins, an isoelectric point in the range 5.2-5.3 and a sedimentation coefficient of 2.7 S. Its molecular weight was determined to be 30 300 by ultracentrifugation and 38 000 by SDS-polyacrylamide gel electrophoresis. PP17 apparently consists of a single peptide chain. The amino acid and carbohydrate compositions of these proteins also have been determined. Immunochemical methods were used to detect and quantitate the new proteins in extracts of placental and other human tissues as well as in body fluids. From one human term placenta an average of 3.7 mg PP13 and 2.5 mg PP17 could be extracted. In concentrated extracts of other human tissues and in body fluids, these proteins could not be detected, at least not in concentrations higher than 1 mg/dl. The immunohistochemical localization of these proteins as well as measurement of their concentrations in body fluids by sensitive radioimmunoassays are presently under investigation.