Posttranslational modification and secretion of vitellogenin in Xenopus laevis
The thesis represents an attempt to elucidate the intracellular pathway linking the synthesis and secretion of the yolk precursor protein vitellogenin. More specifically, how the hepatocyte attaches both phosphate and carbohydrate to the peptide backbone prior to secretion is considered. A model which summarizes the accumulated data depicting various aspects of these processes is also presented. Pulse-chase experiments demonstrate the subcellular sites of vitellogenin phosphorylation. The results of these experiments indicate that approximately 70% of the phsosphate residues are covalently attached to vitellogenin during its intracellular translocation through the smooth microsomes, while the rough microsomes can account for the remainder of the total incorporated phosphate. The presence of a divalent-cation requiring protein kinase (E.C. 2.7.1,37, ATP:protein phosphotransferase) is demonstrated in the microsomes derived from the liver of estrogenized female Xenopus laevis. We present data showing that this protein kinase is responsible for phosphorylating hepatic precursors to serum vitellogenin in vivo. Pulse-chase experiments measuring the rates of incorporation of radiolabeled glucosamine and galactose into intracellular vitellogenin show that glycosylation of this multicomponent protein occurs in a Golgi-enriched fraction isolated from homogenized liver slices. The results indicate that the oligosaccharide component of vitellogenin in Xenopus is a complex type of carbohydrate unit which is linked via an N-glycosidic bond between an asparagine residue and N-acetylglucosamine. With respect to subcellular localization of glycoprotein assembly in Xenopus liver, there is a significant departure from currently accepted models of glycoprotein synthesis.
- Research Organization:
- Tennessee Univ., Knoxville (USA)
- DOE Contract Number:
- AC05-76OR00033
- OSTI ID:
- 6641621
- Report Number(s):
- DOE/NBM-1047; ON: DE83003002
- Resource Relation:
- Other Information: Thesis
- Country of Publication:
- United States
- Language:
- English
Similar Records
Intracellular phosphorylation of vitellogenin in the liver of estrogen-stimulated Xenopus laevis
Characterization of nuclear protein kinases of Xenopus laevis oocytes
Related Subjects
PROTEINS
BIOSYNTHESIS
MOLECULAR STRUCTURE
TRANSLOCATION
BIOLOGICAL PATHWAYS
ENZYME ACTIVITY
FROGS
GLUCOPROTEINS
LIVER CELLS
MICROSOMES
OOCYTES
PHOSPHORYLATION
AMPHIBIANS
ANIMAL CELLS
ANIMALS
AQUATIC ORGANISMS
CARBOHYDRATES
CELL CONSTITUENTS
CHEMICAL REACTIONS
GERM CELLS
ORGANIC COMPOUNDS
ORGANOIDS
SACCHARIDES
SOMATIC CELLS
SYNTHESIS
VERTEBRATES
550200* - Biochemistry