Gluconeogenesis coupled

The first steps of actual gluconeogenesis take place in the mitochondria. The reason for this detour is the equilibrium state of the pyruvate kinase reaction (see p. 150). Even coupling to ATP hydrolysis would not be sufficient to convert pyruvate directly into phos-phoenol pyruvate (PEP). Pyruvate derived... 

The organization of glycolysis and gluconeogenesis as a series of connected metabolic pools makes it possible for most of the same enzymes to function in both directions. Only the reactions connecting the metabolic pools require different enzymes and a coupling to the ATP-ADP system to make them thermodynamically feasible in the direction of gluconeogenesis. 

In gluconeogenesis, the thermodynamic barrier imposed by pyruvate kinase is overcome by coupling two separate reactions for the synthesis of PEP from pyruvate. 

The release of insulin is closely coupled with the glucose level. Hypoglycemia results in a low level of insulin and a high level of glucagon and, hence, favors the processes of glycogenolysis and gluconeogenesis. 

The formation of glucose from pyruvate is energetically unfavorable unless it is coupled to reactions that are favorable. Compare the stoichiometry of gluconeogenesis with that of the reverse of glycolysis. 

Chemistry, mechanism, and effects Glucagon is the product of the A cells of the endocrine pancreas. Like insulin, glucagon is a peptide but unlike insulin, glucagon acts on G protein-coupled receptors. Activation of glucagon receptors, which are located in heart, smooth muscle, and liver, stimulates adenylyl cyclase and increases intracellular cAMP. This results in increases in the heart rate and the force of contraction, increased hepatic glycogenolysis and gluconeogenesis and relaxation of smooth muscle. The smooth muscle effect is particularly marked in the gut. 

In G. xylinus, cellulose synthesis is tightly associated with catabolic processes of oxidation and consumes as much as 10% of energy derived from catabolic reactions. Production of BC does not interfere with other anabohc processes, including protein synthesis. Gluconacetobacter xylinus follows either pentose phosphate cycle or the Krebs cycle coupled with gluconeogenesis (Ross et al., 1991 Tonouchi et al., 1996). 

This conversion of malate to phospho-enolpyruvate (PEP) turned out to be of much interest later, especially thanks to work from Harland Wood s group. It is probably one of the main pathways in gluconeogenesis from pyruvate and COg and Utter and Kurahashi described precisely the coupling between carboxylation-decafboxylation reactions of the pyruvate system and phosphorylation of guanosine diphosphate to triphosphate. ... 

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