The enzyme phosphoglucose isomerase converts glucose 6-phosphate to its isomer fructose 6-phosphate in the second step of glycolysis. The equilibrium constant for the reaction is 0.36. Evaluating the ΔG° of the reaction (ΔG° = -5.9 × log Kₑq), decide which of the following conclusions is true.

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Since the equilibrium constant is less than 1, the log Kₑq term is negative, making the ΔG° positive, which means the reaction is unfavorable under standard conditions. But inside a cell performing glycolysis, a lower concentration of fructose 6-phosphate than of glucose 6-phosphate can drop ΔG to a negative value. The reaction thus proceeds in the forward direction, providing a continuous supply of substrate for the next step in the pathway. Note that due to "coupling" of the reactions in the glycolytic pathway, and even though some steps can have positive ΔG° values, the overall negative ΔG° of the pathway can drive the entire chain of reactions in the forward direction, even under the standard conditions.

The Enzyme Phosphoglucose Isomerase Converts Glucose 6-Phosphate to Its Isomer