In an erythrocyte undergoing glycolysis, what would be the effect of a sudden increase in the concentration of a. ATP? b. AMP? c. fructose-1,6-bisphosphate? d. fructose-2,6-bisphosphate? e. citrate? f. glucose-6-phosphate?

a. ATP​

• ATP acts as an allosteric inhibitor of phosphofructokinase-1 (PFK-1), a key regulatory enzyme in glycolysis.​

• An increase in ATP concentration signals sufficient energy availability, leading to decreased PFK-1 activity and a subsequent slowdown in glycolytic flux.​

• This negative feedback mechanism helps maintain energy homeostasis within the cell.​

b. AMP​

• AMP serves as an allosteric activator of PFK-1.​

• Elevated AMP levels indicate low cellular energy status, prompting an upregulation of glycolysis to generate more ATP.​

• This positive feedback ensures rapid response to energy demands.​

c. Fructose-1,6-bisphosphate (F-1,6-BP)​

• F-1,6-BP is an intermediate in glycolysis that acts as an allosteric activator of pyruvate kinase (PK), enhancing the conversion of phosphoenolpyruvate to pyruvate.​

• An increase in F-1,6-BP concentration accelerates the latter stages of glycolysis, promoting efficient energy production.​

d. Fructose-2,6-bisphosphate (F-2,6-BP)​

• F-2,6-BP is a potent allosteric activator of PFK-1 and an inhibitor of fructose-1,6-bisphosphatase.​

• Elevated levels of F-2,6-BP enhance glycolysis by increasing PFK-1 activity and simultaneously inhibit gluconeogenesis.​

• This dual regulation ensures a coordinated control of glucose metabolism.​

e. Citrate​

• Citrate functions as an allosteric inhibitor of PFK-1.

• An increase in citrate concentration reflects a high level of biosynthetic precursors, signaling to downregulate glycolysis.​

• This inhibition prevents excessive accumulation of metabolic intermediates.​

f. Glucose-6-phosphate (G6P)​

• G6P acts as an allosteric inhibitor of hexokinase, the enzyme catalyzing the first step of glycolysis.​

• Elevated G6P levels indicate a bottleneck in downstream glycolytic steps, leading to feedback inhibition of glucose phosphorylation.​

• This regulation prevents unnecessary consumption of glucose when glycolytic flux is impeded.