Subcellular site of synthesis of the N-acetylgalactosamine (alpha 1-0) serine (or threonine) linkage in rat liver

Journal Article · Wed Mar 25 04:00:00 EST 1987 · J. Biol. Chem.; (United States)

OSTI ID:6528968

Abeijon, C; Hirschberg, C B

We have studied the subcellular site of synthesis of the GalNAc(alpha-1-0) Ser/Thr linkage in rat liver. The specific and total activities of polypeptide:N-acetylgalactosaminyltransferase (using apomucin as exogenous acceptor) were highly enriched in membrane fractions derived from the Golgi apparatus; virtually no activity was detected in membranes from the rough and smooth endoplasmic reticulum. Vesicles of the above organelles (which were sealed and of the same membrane topographical orientation as in vivo) were able to translocate UDP-GalNAc into their lumen in an assay in vitro; the initial translocation rate into Golgi vesicles was 4-6-fold higher than that into vesicles from the rough and smooth endoplasmic reticulum. Translocation of UDP-GalNAc into Golgi vesicles was temperature dependent and saturable with an apparent Km of 8-10 microM. UDP-GalNAc labeled with different radioisotopes in the uridine and sugar was used to determine that the intact sugar nucleotide was being translocated in a reaction coupled to the exit of luminal UMP. Following translocation of UDP-GalNAc, transfer of GalNAc into endogenous macromolecular acceptors was detected in Golgi vesicles and not in those from the rough and smooth endoplasmic reticulum. The above results together with previous studies on the O-xylosylation of the linkage region of proteoglycans strongly suggest that, in rat liver, the bulk of O-glycosylation reactions occur in the Golgi apparatus.

• Research Organization: St. Louis Univ. School of Medicine, MO
• OSTI ID: 6528968
• Journal Information: J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 9; ISSN JBCHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
ANIMALS
BIOCHEMICAL REACTION KINETICS
BODY
CARBOHYDRATES
CARBON COMPOUNDS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
DIGESTIVE SYSTEM
ENDOPLASMIC RETICULUM
ENZYME ACTIVITY
ENZYMES
GLANDS
GLUCOPROTEINS
GLYCOSIDES
GLYCOSYL TRANSFERASES
HYDROXY ACIDS
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LABELLED COMPOUNDS
LIVER
MAMMALS
NUCLEOTIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
ORGANOIDS
ORGANS
PROTEINS
RADIOISOTOPES
RATS
REACTION KINETICS
RODENTS
SACCHARIDES
SERINE
TEMPERATURE DEPENDENCE
THREONINE
TRACER TECHNIQUES
TRANSFERASES
TRITIUM COMPOUNDS
UDPG
VERTEBRATES