These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Effects of ionic strength and chloride ion on activities of the glucose-6-phosphatase system: regulation of the biosynthetic activity of glucose-6-phosphatase by chloride ion inhibition/deinhibition.
    Author: Pederson BA, Nordlie MA, Foster JD, Nordlie RC.
    Journal: Arch Biochem Biophys; 1998 May 01; 353(1):141-51. PubMed ID: 9578609.
    Abstract:
    Certain amino acids stimulate glycogenesis from glucose. The regulatory volume decrease mechanism explaining these effects was defined by Meijer et al. (1992, J. Biol. Chem. 267, 5823-5828). It involves amino acid-induced swelling of hepatocytes resulting in loss of chloride ions which leads to deinhibition of glycogen synthase phosphatase. This results in enhanced conversion of the inactive to active form of glycogen synthase and thus enhanced glycogen synthesis. We have studied the effects of amino acids and chloride ion on the glucose-6-phosphatase system (Glc-6-Pase) with rat liver microsomal preparations, and correlated our results with those reported by others with glycogen synthase. Glc-6-Pase activities are increased by elevated ionic strength varied by increasing the concentration of various buffers or charged amino acids but are not affected by changes in osmolarity, varied with disaccharides or uncharged amino acids. With undisrupted microsomes, chloride ion competitively inhibits carbamyl phosphate: glucose phosphotransferase (KCP,t,UMi,Cl- = 19 mM) more extensively than Glc-6-P phosphohydrolase (KG6P,h,UMi,Cl- = 117 mM). Inhibition by chloride ion and activation due to ionic strength may be important considerations when assessing in vitro Glc-6-Pase activities where an attempt is made to replicate physiologic conditions. Further we propose that amino acids may play a role in increasing biosynthetic activity of Glc-6-Pase, as well as previously characterized glycogen synthase (Meijer et al., op. cit.), via the regulatory volume decrease mechanism through diminished chloride ion inhibition. Reduced concentration of chloride ion will (1) deinhibit the biosynthetic activity of Glc-6-Pase, while still inhibiting Glc-6-P hydrolysis, leading to an increased cellular concentration of Glc-6-P (an important glycogenic intermediate as well as allosteric activator of glycogen synthase) and (2) increase the active form of glycogen synthase by deinhibiting glycogen synthase phosphatase both through the previously defined mechanism (see above) and via Glc-6-P-enhanced conversion of glycogen synthase from its inactive to active form. We propose that the biosynthetic activity of Glc-6-Pase may act in concert with glycogen synthase during amino acid-induced glycogenesis from glucose.
    [Abstract] [Full Text] [Related] [New Search]