Characterization of solubilized microvillous membrane proteins and glycoproteins from human placental syncytiotrophoblast.

Microvillous membrane fractions from human term placentae were prepared by differential centrifugation. Extration of membranes with PBS-EDTA or KCI removed soluble cytoplasmic components and serum proteins excepting trace amounts of albumin and transferrin. PAGE-SDS revealed 11 components in the Triton solubilized crude fraction after PBS-EDTA extraction. Membrane components solubilized with Triton were not fractionated by gel filtration on Bio-Gel A-50 m but DEAE-cellulose chromatography partially resolved these components. Three fractions were obtained by stepwise elution of absorbed materials using increasing concentrations of NaCl in the equilibrating buffer. These fractions were characterized using SDS-PAGE. The material unabsorbed to the DEAE contained two components of small molecular weight and one of them showed a positive PAS stain. The first eluted protein peak showed nine components, seven of which stained with PAS. The bulk of glycoproteins with molecular weights greater than 130 000 daltons were found in this fraction. The second eluted peak from DEAE was rich in components with molecular weights less than 42 000 daltons. Four components in this fraction were not identified in the other two ion-exchange fractions. Bands representing mobilities of albumin, transferrin and alkaline phosphatase were observed in DEAE-cellulose fractions; however, 12 components of unknown structure were revealed.