A major proportion of N-glycoproteins are transiently glucosylated in the endoplasmic reticulum

Journal Article · Tue Mar 26 00:00:00 EST 1991 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00226a017· OSTI ID:5399227

Ganan, S; Cazzulo, J J; Parodi, A J ^[1]

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1. Instituto de Investigaciones Bioquimicas, Buenos Aires (Argentina)

N-Linked, high-mannose-type oligosaccharides lacking glucose residues may be transiently glucosylated directly from UDP-Glc in the endoplasmic reticulum of mammalian, plant, fungal, and protozoan cells. The products formed have been identified as N-linked Glc{sub 1}Man{sub 5-9}GlcNAc{sub 2} and glucosidase II is apparently the enzyme responsible for the in vivo deglucosylation of the compounds. As newly glucosylated glycoproteins are immediately deglucosylated, it is unknown whether transient glucosylation involves all or nearly all N-linked glycoproteins or if, on the contrary, it only affects a minor proportion of them. In order to evaluate the molar proportion of N-linked oligosaccharides that are glucosylated, cells of the trypanosomatid protozoan Trypanosoma cruzi (a parasite transferring Man{sub 9}GlcNAc{sub 2} in protein N-glycosylation) were grown in the presence of ({sup 14}C)glucose and concentrations of the glucosidase II inhibitors deoxynojirimycin and castanospermine that were more than 1,000-fold higher than those required to produce a 50% inhibition of the T. cruzi enzyme. No evidence for the presence of an endomannosidase yielding GlcMan from the glucosylated compounds was obtained. As the average number of N-linked oligosaccharides per molecule in glycoproteins is higher than one, these results indicate that more than 52-33% of total glycoproteins are glucosylated and that transient glucosylation is a major event in the normal processing of glycoproteins.

• OSTI ID: 5399227
• Journal Information: Biochemistry; (United States), Vol. 30:12; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
ENDOPLASMIC RETICULUM
ENZYME ACTIVITY
GLYCOPROTEINS
BIOCHEMISTRY
OLIGOSACCHARIDES
CARBON 14 COMPOUNDS
CELL MEMBRANES
GLUCOSE
GLUCOSIDASE
MANNOSE
SPERMINE
TRYPANOSOMA
ALDEHYDES
AMINES
ANIMALS
CARBOHYDRATES
CARBON COMPOUNDS
CELL CONSTITUENTS
CHEMISTRY
ENZYMES
GLYCOSYL HYDROLASES
HEXOSES
HYDROLASES
INVERTEBRATES
LABELLED COMPOUNDS
MASTIGOPHORA
MEMBRANES
MICROORGANISMS
MONOSACCHARIDES
O-GLYCOSYL HYDROLASES
ORGANIC COMPOUNDS
PARASITES
PROTEINS
PROTOZOA
SACCHARIDES
550201* - Biochemistry- Tracer Techniques