Elaborate on how the redox state of the plastoquinone pool influences the activity of fructose‑1,6‑bisphosphatase during the Calvin cycle, including the roles of NADPH and ATP in this regulation.
Answer
A reduced plastoquinone pool enhances fructose‑1,6‑bisphosphatase activity by increasing NADPH production and ensuring ATP availability, whereas an oxidised pool suppresses it.
Step-by-step solution
- When the PQ pool is reduced (PQH₂), electron transport is active and NADPH is abundant.
- High NADPH levels favor the reduction steps of the Calvin cycle and activate fructose‑1,6‑bisphosphatase.
- Simultaneously, ATP is being consumed in carboxylation; a reduced PQ pool signals sufficient ATP for the cycle to proceed.
- If the PQ pool is oxidised, electron transport slows, NADPH drops, and ATP synthesis is limited, thereby down‑regulating fructose‑1,6‑bisphosphatase activity.
- Thus, the redox state of PQ indirectly controls the enzyme through the availability of NADPH and ATP.
Common mistake: Attributing regulation solely to NADPH and ignoring ATP
Concept tested: Regulation of Calvin cycle by redox state
Published · How this solution was prepared and checked
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