Subcellular site of synthesis of the N-acetylgalactosamine (alpha 1-0) serine (or threonine) linkage in rat liver
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), Vol. 9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GLUCOPROTEINS
BIOCHEMICAL REACTION KINETICS
SERINE
THREONINE
CARBON COMPOUNDS
ENDOPLASMIC RETICULUM
ENZYME ACTIVITY
GLYCOSYL TRANSFERASES
LIVER
ORGANOIDS
RADIOISOTOPES
RATS
TEMPERATURE DEPENDENCE
TRACER TECHNIQUES
TRITIUM COMPOUNDS
UDPG
AMINO ACIDS
ANIMALS
BODY
CARBOHYDRATES
CARBOXYLIC ACIDS
CELL CONSTITUENTS
DIGESTIVE SYSTEM
ENZYMES
GLANDS
GLYCOSIDES
HYDROXY ACIDS
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LABELLED COMPOUNDS
MAMMALS
NUCLEOTIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
ORGANS
PROTEINS
REACTION KINETICS
RODENTS
SACCHARIDES
TRANSFERASES
VERTEBRATES
550201* - Biochemistry- Tracer Techniques