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Hormonal induction of the phosphorylation of the glycogen synthase isolated from Xenopus laevis (Daudin) oocytes
Baras, B.; Debauche, P.; Devos, P. (1993). Hormonal induction of the phosphorylation of the glycogen synthase isolated from Xenopus laevis (Daudin) oocytes. Belg. J. Zool. 123(Suppl. 1): 5
In: Belgian Journal of Zoology. Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Gent. ISSN 0777-6276, more
Peer reviewed article  

Also published as
  • Baras, B.; Debauche, P.; Devos, P. (1993). Hormonal induction of the phosphorylation of the glycogen synthase isolated from Xenopus laevis (Daudin) oocytes, in: Chardon, M. et al. (Ed.) Third Belgian Congress of Zoology, 5-6 November 1993. Belgian Journal of Zoology, 123(Suppl. 1): pp. 5, more

Available in Authors 
    VLIZ: Proceedings [39377]
Document type: Summary

Keywords
    Biochemical phenomena; Embryonic development; Enzymatic activity; Glycogen; Hormones; Oocytes; Amphibia [WoRMS]; Xenopus laevis; Fresh water

Authors  Top 
  • Baras, B.
  • Debauche, P.
  • Devos, P.

Abstract
    The oocyte of Xenopus laevis is a unicellular structure whose fecondation and segmentation take place in the outer medium. Therefore it accumulates reserves during its intraovarian development, among these glycogen. We were interested in the molecular mechanisms leading to the regulation of its synthesis and degradation. In this framework, we focused our attention on the regulation of glycogen synthase, the main enzyme implicated in glycogen biosynthesis. To begin with, we purified this enzyme 1,500 fold, using high speed centrifugation and two types of chromatography: an ion-exchange (DEAE-Cellulose) chromatography and an affinity chromatography for glucose-6-phosphate, a potent stimulator of glycogen synthase. After electrophoresis and silver staining, the estimated molecular weight of the subunit of the purified enzyme is 85 kD. Our second step was to investigate how the process of phosphorylation- dephosphorylation controls glycogen synthase activity. First we showed that the enzyme is inhibited by cAMP-dependent phosphorylation and can be found as a phosphoenzyme in an autoradiographic pattern. In addition, experiments making use of thin layer chromatography are currently in progress to demonstrate that the phosphorylation sites are located on serine residues. Finally, we studied the hormonal induction of glycogenosynthesis during the oogenesis of Xenopus laevis. First we demonstrated that insulin stimulates both glucose transport across the oocyte membrane and its incorporation into glycogen. Moreover, following insulin treatment, glycogen synthase is fully converted into its active form, while the phosphorylation rates are largely reduced, particularly among the proteins associated with a glycogen-rich preparation. These results confirm the previous data showing that the effect of insulin leads to a drastic decrease in cAMP levels via the inhibition of adenylate cyclase and the activation of membrane-bound phosphodiesterases.

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