Localization of protein-bound carbohydrate residues on the cytoplasmic surface of rough and smooth microsomes and Golgi vesicles from rat liver.

Rough and smooth microsomes and Golgi membranes isolated from rat liver were treated with proteolytic enzymes under conditions which removed 30--40% of the surface proteins without seriously disrupting the membrane structure. This treatment also removed 40--60% of protein-bound mannose, galactose and glucosamine. When protease treatment was combined with neuraminidase treatment, 80% of the sialic acid was removed from intact rough microsomal and Golgi vesicles and about half of the sialic acid of smooth microsomes was solubilized. It appears that half, or probably more, of the membrane glycoproteins are associated with the cytoplasmic surface of these membranes.