Glucose 6-phosphate plays a central role in the regulation of glycogen synthesis in a glycogen-storing liver cell line
✍ Scribed by D. Mayer; I. Letsch
- Publisher
- John Wiley and Sons
- Year
- 1989
- Tongue
- English
- Weight
- 910 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0263-6484
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✦ Synopsis
Two substrains of the epithelial liver cell line C1 I, one storing large amounts of glycogen, the other one being very poor in glycogen were used as a model for studying glycogen synthesis. The glycogen content of glycogen-rich cells doubled during the proliferative phase and remained high in plateau phase although glycogen synthase I activity was not significantly altered during growth cycle and was too low to account for the increase in glycogen. However, the activity of the glucose 6-phosphate (Glc6-P)-dependent synthase rose continuously during growth cycle, and intracellular Glc6-P-concentration increased about 10-fold in log phase cells to 0.72 pmol g-' wet weight.
of synthase for Glc6-P was 0 . 7 9 m ~. It was also found that in contrast to the enzyme from normal liver, glycogen phosphorylase a from C, I cells was inhibited by Glc6-P, the apparent Ki being 0.45 mM. It was concluded that glycogen accumulation in CII cells was due to stimulation of synthase and inhibition of phosphorylase by Glc6-P. Findings from the glycogen-poor cell line which revealed similar specific activities of synthase and phosphorylase but only low Glc6-P (0.056 pmol g-' wet weight) supported this conclusion. Addition of glucose to starved cells resulted in a transient activation of synthase in both cell lines. Net glycogen synthesis, was, however, only obsened in the cells with a high Glc6-P-content. Thus, modulation of synthase and phosphorylase by Glc6-P and not activatiodinactivation of the enzymes seems to play a predominant role in glycogen accumulation in this cell line.