Chapter 18

(Integrates with Chapter 3 .) Enolase catalyzes the conversion of 2-phosphoglycerate to phosphoenolpyruvate \(+\mathrm{H}_{2} \mathrm{O}\). The standard free energy change, \(\Delta G^{\circ},\) for this reaction is \(+1.8 \mathrm{kJ} / \mathrm{mol}\). If the concentration of 2 -phosphoglycerate is \(0.045 \mathrm{m} M\) and the concentration of phosphoenolpyruvate is \(0.034 \mathrm{m} M\), what is \(\Delta G\), the free energy change for the enolase reaction, under these conditions?

(Integrates with Chapter \(3 .)\) The standard free energy change \(\left(\Delta G^{\circ \prime}\right)\) for hydrolysis of phosphoenolpyruvate (PEP) is \(-61.9 \mathrm{kJ} / \mathrm{mol}\) The standard free energy change \(\left(\Delta G^{\circ \prime}\right)\) for ATP hydrolysis is \(-30.5 \mathrm{kJ} / \mathrm{mol}\) a. What is the standard free energy change for the pyruvate kinase reaction: ADP \(+\) phosphoenolpyruvate \(\longrightarrow\) ATP \(+\) pyruvate b. What is the equilibrium constant for this reaction? c. Assuming the intracellular concentrations of [ATP] and [ADP] remain fixed at \(8 \mathrm{m} M\) and \(1 \mathrm{m} M\), respectively, what will be the ratio of [pyruvate]/[phosphoenolpyruvate] when the pyruvate kinase reaction reaches equilibrium?

(Integrates with Chapter \(3 .)\) The standard free energy change \(\left(\Delta G^{\circ \prime}\right)\) for hydrolysis of fructose- 1,6 -bisphosphate (FBP) to fructose6-phosphate (F-6-P) and \(\mathrm{P}_{\mathrm{i}}\) is \(-16.7 \mathrm{kJ} / \mathrm{mol}\) \\[ \mathrm{FBP}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \text { fructose- } 6-\mathrm{P}+\mathrm{P}_{\mathrm{i}} \\] The standard free energy change \(\left(\Delta G^{\circ \prime}\right)\) for ATP hydrolysis is \(-30.5 \mathrm{kJ} / \mathrm{mol}\) \\[ \mathrm{ATP}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{ADP}+\mathrm{P}_{\mathrm{i}} \\] a. What is the standard free energy change for the phosphofructokinase reaction: \\[ \text { ATP + fructose- } 6 \text { -P } \longrightarrow \mathrm{ADP}+\mathrm{FBP} \\] b. What is the equilibrium constant for this reaction? c. Assuming the intracellular concentrations of [ATP] and [ADP] are maintained constant at \(4 \mathrm{m}\) Mand \(1.6 \mathrm{m} M\), respectively, in a rat liver cell, what will be the ratio of [FBP]/[fructose-6-P] when the phosphofructokinase reaction reaches equilibrium?

Fructose bisphosphate aldolase in animal muscle is a class I aldolase, which forms a Schiff base intermediate between substrate (for example, fructose- 1,6 -bisphosphate or dihydroxyacetone phosphate and a lysine at the active site (see Figure 18.12 ). The chemical evidence for this intermediate comes from studies with aldolase and the reducing agent sodium borohydride, \(\mathrm{NaBH}_{4}\). Incubation of the enzyme with dihydroxyacetone phosphate and \(\mathrm{NaBH}_{4}\) inactivates the enzyme. Interestingly, no inactivation is observed if \(\mathrm{NaBH}_{4}\) is added to the enzyme in the absence of substrate. Write a mechanism that explains these observations and provides evidence for the formation of a Schiff base intermediate in the aldolase reaction.

As noted on page 556 , the galactose- 1 -phosphate uridylyltransferase reaction proceeds via a ping-pong mechanism. Consult Chapter 13 page \(406,\) to refresh your knowledge of ping-pong mechanisms, and draw a diagram to show how a ping-pong mechanism would proceed for the uridylyltransferase.

Genetic defects in glycolytic enzymes can have serious consequences for humans. For example, defects in the gene for pyruvate kinase can result in a condition known as hemolytic anemia. Consult a reference to learn about hemolytic anemia, and discuss why such genetic defects lead to this condition.

Regarding phosphofructokinase, which of the following statements is true: a. Low ATP stimulates the enzyme, but fructose- 2,6 -bisphosphate inhibits. b. High ATP stimulates the enzyme, but fructose- 2,6 -bisphosphate inhibits. c. High ATP stimulates the enzyme, but fructose- 2,6 -bisphosphate inhibits. d. The enzyme is more active at low ATP than at high, and fructose- 2,6 -bisphosphate activates the enzyme. e. ATP and fructose- 2,6 -bisphosphate both inhibit the enzyme.

Based on your reading of this chapter, what would you expect to be the most immediate effect on glycolysis if the steady-state concentration of glucose- 6 -P were \(8.3 \mathrm{m}\) M instead of \(0.083 \mathrm{mM}\) ?