Cell‐Free Synthesis and Glycosylatlon of the Major Human‐Red‐Cell Sialoglycoprotein, Glycophorin A

Abstract

The human erythroid cell line, K562, synthesizes the major red cell sialoglycoprotein, glycophorin A. An mRNA fraction which codes for glycophorin A was isolated from K562 cells and studied the synthesis of the sialoglycoprotein in a rabbit reticulocyte cell-free system. In the absence of membranes a precursor form of glycophorin A was synthesized. This was identified using specific anti-(glycophorin A) serum. The apparent MW of the carbohydrate-free precursor of glycophorin A was 19,500. This exceeds the MW of the glycophorin A apoprotein by .apprx. 5000. In the presence of membranes from dog pancreas, the synthesized glycophorin A precursor was N-glycosylated and probably also O-glycosylated. The oligosaccharide chains remained incompleted and the glycoprotein synthesized in vitro corresponded to the glycosylated precursor of glycophorin A obtained in intact cells.