The Role of the Regulatory Protein of Glucokinase in the Glucose Sensory Mechanism of the Hepatocyte
| Autor: | Mohammed H. Mukhtar, Joan Seoane, Núria de la Iglesia, Loranne Agius, Joan J. Guinovart |
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| Rok vydání: | 2000 |
| Předmět: |
Male
medicine.medical_specialty Genetic Vectors Carbohydrate metabolism Biology Biochemistry Adenoviridae chemistry.chemical_compound Internal medicine Glucokinase medicine Animals Sorbitol Glycolysis Rats Wistar Glycogen synthase Molecular Biology Cells Cultured Sensory mechanism Glucokinase regulatory protein Gene Transfer Techniques Intracellular Signaling Peptides and Proteins Proteins Cell Biology Recombinant Proteins Liver Glycogen Rats Kinetics Glucose medicine.anatomical_structure Endocrinology Liver chemistry Hepatocyte biology.protein Carrier Proteins |
| Zdroj: | Journal of Biological Chemistry. 275:10597-10603 |
| ISSN: | 0021-9258 0479-3048 |
| Popis: | Glucokinase has a very high flux control coefficient (greater than unity) on glycogen synthesis from glucose in hepatocytes (Agius et al., J. Biol. Chem. 271, 30479-30486, 1996). Hepatic glucokinase is inhibited by a 68-kDa glucokinase regulatory protein (GKRP) that is expressed in molar excess. To establish the relative control exerted by glucokinase and GKRP, we applied metabolic control analysis to determine the flux control coefficient of GKRP on glucose metabolism in hepatocytes. Adenovirus-mediated overexpression of GKRP (by up to 2-fold above endogenous levels) increased glucokinase binding and inhibited glucose phosphorylation, glycolysis, and glycogen synthesis over a wide range of concentrations of glucose and sorbitol. It decreased the affinity of glucokinase translocation for glucose and increased the control coefficient of glucokinase on glycogen synthesis. GKRP had a negative control coefficient of glycogen synthesis that is slightly greater than unity (-1.2) and a control coefficient on glycolysis of -0.5. The control coefficient of GKRP on glycogen synthesis decreased with increasing glucokinase overexpression (4-fold) at elevated glucose concentration (35 mM), which favors dissociation of glucokinase from GKRP, but not at 7.5 mM glucose. Under the latter conditions, glucokinase and GKRP have large and inverse control coefficients on glycogen synthesis, suggesting that a large component of the positive control coefficient of glucokinase is counterbalanced by the negative coefficient of GKRP. It is concluded that glucokinase and GKRP exert reciprocal control; therefore, mutations in GKRP affecting the expression or function of the protein may impact the phenotype even in the heterozygote state, similar to glucokinase mutations in maturity onset diabetes of the young type 2. Our results show that the mechanism comprising glucokinase and GKRP confers a markedly extended responsiveness and sensitivity to changes in glucose concentration on the hepatocyte. |
| Databáze: | OpenAIRE |
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