Glucose 6-phosphate effector

A metabolite acting as an allosteric effector turns on an enzyme that either acts directly on that metabolite or acts on a product that lies further ahead in the sequence. For example, in Fig. 11-1, metabolite C activates the enzyme that catalyzes an essentially irreversible reaction of compound D. An actual example is provided by glycogen synthase, whose inactive "dependent" or D form is activated allosterically by the glycogen precursor glucose 6-phosphate.39 See also phosphorylase kinase (Section 2). 

Under normal conditions the activity of glycogen phosphorylase (phosphorylase a) is regulated by the cellular concentration of glucose 6-phosphate, ATP, and AMP the first two effectors inhibit its activation, and the third promotes its activation. 

Blood this step because, under conditions that favor gluconeogenesis, the concentrations of the compounds that activate the glycolytic enzyme PFK-1 are low. These same compounds, fructose 2,6-bisphosphate (whose levels are regulated by insulin and glucagon) and AMP, are allosteric inhibitors of fructose 1,6-bisphosphatase. When the concentrations of these allosteric effectors are low, PFK-1 is less active, fructose 1,6-bisphosphatase is more active, and the net flow of carbon is toward fructose 6-phosphate and, thus, toward glucose. The synthesis of fructose 1,6-bisphosphatase is also induced during fasting. 

Increased level of inorganic phosphate leads to a rise in total adenylate level (28) which favours the oxidative phosphorylation and promotes phosphorylation and further carbohydrate metabolism, As in the case Of glucose and other rapidly metabolized substrates, this results in an accumulation of inhibitory catabolites. The mechanism of inhibitory effect of inorganic phosphate may be identical with that of catabolite repression. The action of some positive effectors of secondary metabolite synthesis which also abolish the inhibitory effect of inor-... 

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