Glucose allosteric regulation

Figure 3.29 Control of an enzyme activity by multiple allosteric regulators. The enzyme glycogen phosphorylase b in muscle is regulated by changes in the concentrations of AMP and inosine monophosphate (IMP) (which are activators) and ATP and glucose 6-phosphate (G6P), which are inhibitors.

Skeletal muscle glycogen delivers glucose primarily as a response to contractile stress. Regulation occurs through both modification of the enzyme phosphorylase, primarily by the action of epinephrine-adrenaline and allosteric regulation of phosphorylase related to a demand for ATP. 

FIGURE 20-25 Sucrose synthesis. Sucrose is synthesized from UDP-glucose and fructose 6-phosphate, which are synthesized from triose phosphates in the plant cell cytosol by pathways shown in Figures 15-7 and 20-9. The sucrose 6-phosphate synthase of most plant species is allosterically regulated by glucose 6-phosphate and P,. 

Figure 21.12. Allosteric Regulation of Liver Phosphorylase. The binding of glucose to phosphorylase a shifts the equilibrium to the T state and inactivates the enzyme. Thus, glycogen is not mobilized when glucose is already abundant.

Sebastian S, Wilson JE, Muhchak A, Garavito RM. Allosteric regulation of type I hexokinase A site-directed mutational study indicating location of the functional glucose 6-phosphate binding site in the N-terminal half of the enzyme. Arch Biochem Biophys 1999 362 203-10. 

Other biotin-dependent enzymes include propionyl-CoA carboxylase and pyruvate carboxylase (Chapter 15). The latter, like acetyl-CoA carboxylase, is subject to allosteric regulation. Pyruvate carboxylase, a mitochondrial enzyme, is activated by acetyl-CoA and converts pyruvate to oxaloacetate which, in turn, is converted to glucose via... 

This reaction is catalyzed by the enzyme fructose-l,6-hisphosphatase, an allosteric enzyme strongly inhibited by adenosine monophosphate (AMP) but stimulated by ATP. Because of allosteric regulation, this reaction is also a control point in the pathway. When the cell has an ample supply of ATP, the formation rather than the breakdown of glucose is favored. This enzyme is inhibited by fructose-2,6- >t5phosphate, a compound we met in Section 17.2 as an extremely potent activator of phosphofructokinase. We shall return to this point in the next section. 

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