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Abstract

Coated vesicles were isolated from rat liver by a modification of the procedure described by Nandi et al. for bovine brain (Proc. Natl. Acad. Sci. U.S.A. 1982; 79:5881–5885). The hepatic receptor for asialoglycoproteins was shown to be an integral constitutent of these vesicles as evidenced by their ability to bind 125I-asialo-orosomucoid in a specific and saturable manner. The specific binding activity of the purified vesicles was 17-fold greater than that of the original liver homogenate based on a protein determination. Binding was 97% latent and was made fully manifest only after removal of the clathrin coat and disruption of the exposed smooth membrane vesicles by detergent. Based on this finding, it was concluded that the binding protein for asialoglycoproteins was oriented toward the inner surface of the vesicle. In addition, evidence is presented that purification procedures employing detergent may result in coated vesicles deficient in one or more integral membrane proteins.