Glycosylation of a receptor specific for asialoglycoproteins in rat liver

Glycosylation of a rat receptor specific for asialoglycoproteins was investigated in vivo by using monospecific antibody. After intravenous injection of [3H]mannose, the receptor protein was immunoprecipitated from various subcellular fractions and the glycopeptide and oligosaccharide chains of the protein were prepared by treatment with pronase and endo-beta-N-acetylglucosaminidase H. The glycopeptides thus prepared from the rough and smooth microsomes and Golgi heavy fraction (GF3) were all sensitive to endo H and most of the endo H-sensitive oligosaccharides were eluted at the position considered to correspond to Man8GlcNAc on high-resolution Bio-Gel chromatography. Endo H-resistant forms were first detected in the Golgi intermediate fraction (GF2) and significantly in the light Golgi fraction (GF1), suggesting the formation of the complex-type oligosaccharide chains in the latter fraction. This view was also supported by the almost exclusive addition of the terminal sugars such as N-acetylglucosamine, galactose, and sialic acid in GF1. These results suggest that the major form of the oligosaccharide chains from the endoplasmic reticulum to the Golgi apparatus is Man8GlcNAc2 and that the processing of these large mannosyloligosaccharide chains and subsequent addition of terminal sugars to them are performed successively in the trans-Golgi region.