Abstract
Previous work in this laboratory [I] has demonstrated that the structural protein fraction prepared from rat liver microsomes consists of glycoproteins with 1.5% of the carbohydrate moieties made up of mannose, galactose, glucose, hexosamine and sialic acid. For chemical characterization of the carbohydrate moieties we attempted to isolate glycopeptides by proteolytic digestion. Two types of glycopeptides, i.e. one with acidic and another with neutral oligosaccharides, could be isolated. They apparently resembled those isolated by Li et al. [2 ] from an unfractionated membranous fraction of microsomes but differed significantly in carbohydrate composition from the latter. The microsomal structural protein fraction is derived largely from proteins of endoplasmic reticulum and partly from those of plasma membranes, Although they could not be separated from each other due to close similarity in gross chemical and physical properties [l] , it seemed interesting to see if each type of oligosaccharide mentioned above might correspond to each membrane structure. There are a few methods available for isolation of plasma membranes with a high degree of purity directly from rat liver homoge-
Published Version
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