Water-soluble proteins of the human red cell membrane

Procedures were developed for preparation of red cell membranes almost free of hemoglobin but with minimal loss of membrane proteins. Two water-soluble protein fractions are described, each constituting about 25% of the ghost protein. The first is ionically bonded and can be solubilized in water rapidly at pH 7.0 and more slowly at higher ionic strength solutions, with a minimal rate at 20MM. This fraction contains four major components with molecular weights ranging from 30,000 to 48,000. The second fraction can only be solubilized at an appreciable rate if Ca(++) is absent and at higher pH (9.0). It is predominantly a single molecular weight component (150,000). It tends to aggregate at higher ionic strength and in the presence of Ca(++). Evidence is presented suggesting that the water-soluble proteins are present at the inner face of the membrane. The lipids remain in a water-insoluble residue that contains four major protein components ranging in molecular weight from 30,000 to 100,000. The latter is the predominant component. Only the residue contains the Na(+)-K(+)-activated ATPase, the cholinesterase, antigenic activity and most of the sialic acid and carbohydrate. The first water-soluble fraction contains a Mg(++)-activated ATPase. The extraction of the water-soluble proteins is accompanied by anatomical changes resulting finally in the formation of small membranous vesicles.