Characterisation of the soluble fraction of human syncytiotrophoblast microvillous plasma membrane-associated proteins

Syncytiotrophoblast microvillous plasma membrane (StMPM) preparations were obtained from human full-term placentae by previously published methods of cold saline extraction and phase centrifugation. Purity of these preparations was assessed by electron microscopy, enzyme analysis and hydroxyproline content. IgG, albumin, alkaline phosphatase, transferrin, ferritin and α 2-macroglobulin were consistently detected in the aqueous soluble fraction from sodium deoxycholate-solubilised StMPM preparations by antigenic or electrophoretic analysis. β 2-Microglobulin was not detected in these preparations. Up to 21 discrete protein bands could be demonstrated by SDS-PAGE, and their molecular weights determined. Many of these components need to be further identified, including a glycoprotein of molecular weight 36 500 which was particularly prominent. The soluble fraction from StMPM preparations gave a single strong precipitin reaction in immunodiffusion against wheat germ agglutinin, but not against other lectins studied.