Properties of an erythrocyte membrane lipoprotein fraction

Abstract

Membrane vesicles and fragments were prepared from ghosts of red blood cells by extracting the water soluble proteins (50 % of the total). On incubation in 8 M urea, about half of the remaining protein and of the lipid could be extracted. The remaining lipid (50 % of the total in the ghost) and protein (25 % of the total in the ghost) were present in small membrane fragments that could be sedimented by centrifugation at high speed. The protein of the pellet was solubilized by use of detergents. The major component (over 80% of the total) has a molecular weight of 95 000 determined by gel electrophoresis. It contains most of the protein bound hexose of the ghost and lesser amounts of other sugars. It is intensively labelled by application of non-penetrating protein reagents to the intact cell, and is presumably located, at least in part, on the outer face of the membrane. The lipids associated with the urea pellet were not essentially different from those of the original ghost. It is suggested that a small fraction of the lipid is hydrophobically bonded to the pellet protein and that the remainder is held by lipid-lipid interactions.