Question

Which set of conditions would favor glycolysis in the reaction of fructose 6-phosphate and fructose 1,6-bisphosphate?

1. high concentrations of ATP, Cirate and hydrogen ion

2. low concentrations of ATP, Cirate and hydrogen ion

3. high concentrations of acetyle CoA

4. low concentrations of glucose

Answer 1

The correct answer is 2 i.e . Low concentration of ATP,citrate and hydrogen ions favours the reaction fructose -6-phosphate to Fructose-1,6-bisphosphate ,which is catalysed by enzyme phosphofructokinase.

High levels of ATP allosterically inhibit the enzyme (phosphofructokinase)in the liver, thus lowering its affinity for fructose 6-phosphate. ATP elicits this effect by binding to a specific regulatory site that is distinct from the catalytic site. AMP reverses the inhibitory action of ATP, and so the activity of the enzyme increases when the ATP/AMP ratio is lowered. In other words, glycolysis is stimulated as the energy charge falls. A fall in pH also inhibits phosphofructokinase activity. The inhibition of phosphofructokinase by H+ prevents excessive formation of lactic acid and a precipitous drop in blood pH (acidosis).

phosphofructokinase is inhibited by citrate, an early intermediate in the citric acid cycle . A high level of citrate means that biosynthetic precursors are abundant and additional glucose should not be degraded for this purpose. Citrate inhibits phosphofructokinase by enhancing the inhibitory effect of ATP.