Structure of the glycosylphosphatidylinositol membrane anchor of human placental alkaline phosphatase

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Abstract
The glycosylphosphatidylinositol membrane anchor of human placental alkaline phosphatase was isolated by exhaustive proteolysis followed by hydrophobic interaction chromatography. The resulting glycosylphosphatidylinositol-peptide was subjected to compositional analysis and chemical and enzymic modifications. The neutral-glycan fraction, prepared by dephosphorylation followed by HNO2 deamination and reduction, was sequenced using exoglycosidases and acetolysis. The phosphatidylinositol moiety was analysed by fast-atom bombardment mass spectrometry and gas chromatography-mass spectrometry. Taken together the data suggest the structure, Thr-Asp-ethanolamine-PO4-Man alpha 1-2Man alpha 1-6Man alpha 1-4GlcN-(sn-1-O- alkyl-2-O-acylglycerol-3-PO4-1-myo-D-inositol), which contains an additional ethanolamine phosphate group at an unknown position.