Proteins of human placental microvilli: II. Identification and topology of the plasma membrane proteins.
We have investigated the location of proteins in the transverse plane of the plasma membrane of microvilli isolated from the syncytiotrophoblast layer of the human term placenta. Microvillous proteins were labelled with 125I under reaction conditions where those proteins exposed on the maternal-facing surface of the microvilli were most heavily labelled. The proteins were then solubilized and subjected to one- and two-dimensional electrophoresis followed by protein staining and autoradiography. More than 65 proteins, differing in molecular weight or isoelectric point or both, were identified, and these were classified into three groups: weakly, moderately heavily, and heavily labelled. The microvilli were in the form of intact vesicles that were correctly orientated ('right-side out'). Thus the extent of labelling of each protein could be used as an indication of the extent of its exposure on the maternal-facing surface of the microvilli. Human serum albumin was present on the surface of the isolated, washed microvilli, but was probably a contaminant originating from maternal blood.
D000469:Alkaline Phosphatase; D002824:Chorionic Villi / Q000032:analysis* / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D058851:GPI-Linked Proteins; D006801:Humans; D007457:Iodine Radioisotopes; D007527:Isoenzymes / Q000032:analysis; D008565:Membrane Proteins / Q000032:analysis*; D008871:Microvilli / Q000032:analysis; D008970:Molecular Weight; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000032:analysis*; D012995:Solubility; D014168:Transferrin / Q000032:analysis
D058851:GPI-Linked Proteins; D007457:Iodine Radioisotopes; D007527:Isoenzymes; D008565:Membrane Proteins; D011257:Pregnancy Proteins; D014168:Transferrin; D011092:Polyethylene Glycols; D017830:Octoxynol; D000469:Alkaline Phosphatase; C019839:alkaline phosphatase, placental