³¹P Nuclear Magnetic Resonance Evidence for Polyphosphoinositide Associated with the Hydrophobic Segment of Glycophorin A

Glycophorin A, the major human erythrocyte sialoglycoprotein, contains a significant amount of phosphorus when isolated by the lithium diiodosalicylate-phenol procedure. Only a small percentage (approximately 1%) of this phosphorus is phosphoprotein. ³¹P nuclear magnetic resonance (NMR) analysis of glycophorin A has identified the remaining phosphorus content as phospholipid in origin. From the ³¹P chemical shifts, the phospholipid has been identified as diphosphoinositide. ³¹P NMR spectra of the peptides produced by trypsin hydrolysis of glycophorin A reveal that all the diphosphoinositide is closely associated with the hydrophobic region of the protein, suggesting that there is a specific affinity between this phospholipid and the intramembranous portion of glycophorin A.