Intrinsic membrane glycoproteins with cytosol-oriented sugars in the endoplasmic reticulum

Journal Article · Mon Feb 01 04:00:00 EST 1988 · Proc. Natl. Acad. Sci. U.S.A.; (United States)

DOI:https://doi.org/10.1073/pnas.85.4.1010· OSTI ID:6659423

Abeijon, C; Hirschberg, C B

The authors have examined the topography of N-acetylglucosamine-terminating glycoproteins in membranes from rat liver smooth and rough endoplasmic reticulum (SER and RER). It was found that some of these glycoproteins are intrinsic membrane proteins with their sugars facing the cytosolic rather than the luminal side. This conclusion was reached by using vesicles from the SER and RER that were sealed and of the same topographical orientation as in vivo. These vesicles were incubated with UDP-(/sup 14/C)galactose (which does not enter the vesicles) and saturating amounts of soluble galactosyltransferase from milk, an enzyme that does not penetrate the lumen of the vesicles and that specifically adds galactose to terminal N-acetylglucosamine in a ..beta..1-4 linkage. Radioactive galactose was mainly transferred to SER proteins of apparent molecular mass 56 and 110 kDa and to a lesser extent RER and SER proteins of apparent molecular mass 46 and 72 kDa. These proteins are intrinsic membrane proteins, based on the inability of sodium carbonate at pH 11.5 to remove them from the membranes. Studies with peptide N-glycosidase F and chemical ..beta..-elimination showed that the 56-kDa protein of the SER vesicles contained terminal N-acetylglucosamine in an O-linkage to the protein. The above results suggest that some sugars of glycoproteins in the endoplasmic reticulum may attain their final orientation in the membrane by mechanisms yet to be determined.

• Research Organization: Univ. of Massachusetts Medical Center, Worcester (USA)
• OSTI ID: 6659423
• Journal Information: Proc. Natl. Acad. Sci. U.S.A.; (United States), Journal Name: Proc. Natl. Acad. Sci. U.S.A.; (United States) Vol. 85:4; ISSN PNASA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALDEHYDES
ANIMALS
AUTORADIOGRAPHY
BIOCHEMISTRY
BODY
CARBOHYDRATES
CARBON 14 COMPOUNDS
CELL CONSTITUENTS
CELL MEMBRANES
CHEMISTRY
CYTOPLASM
DIGESTIVE SYSTEM
ELECTROPHORESIS
ENDOPLASMIC RETICULUM
GALACTOSE
GLANDS
GLUCOPROTEINS
GLYCOPROTEINS
HEXOSES
LABELLED COMPOUNDS
LIVER
MAMMALS
MEMBRANES
MONOSACCHARIDES
ORGANIC COMPOUNDS
ORGANOIDS
ORGANS
PROTEINS
PURIFICATION
RATS
RODENTS
SACCHARIDES
TOPOGRAPHY
VERTEBRATES