title: The formation of glycosidic bonds in yeast glycoproteins. Intracellular localisation of the reactions.
abstract: Membranes of Saccharomyces cerevisiae were separated on urografin gradients. The specific activity of the light membranes (endoplasmic reticulum), the Golgi-like vesicles and the plasma membrane in transferring mannosyl residues from GDP-mannose to mannoproteins and to dolichyl monophosphate has been determined. The first mannose of the O-glycosidically linked manno-oligosaccharides is incorporated with the highest specific activity by the endoplasmic reticulum. The incorporation of the second to fourth mannosyl groups is catalysed with increasing activity also by the Golgi-like vesicles  and the plasma membrane. The incorporation of mannosyl groups into weak alkali-stable positions (N-glycosidically linked chains) is carried out with almost the same specific activity by all three membrane fractions, however, dolichol-dependent and -independent steps could not be distinguished as yet. The results are discussed in terms of a sequential addition of sugar residues along the route of export of the mannoprotiens. The dolichol-dependent steps seem to occur on the endoplasmic reticulum and thus very early in the event.
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000096:biosynthesis*; D006023:Glycoproteins / Q000096:biosynthesis*; D006056:Golgi Apparatus / Q000378:metabolism; D008358:Mannose / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D013347:Subcellular Fractions
chemical_list: D005656:Fungal Proteins; D006023:Glycoproteins; D008358:Mannose