Question

Predict the effect of adding myxothiazol, an inhibitor of electron transport in mitochondrial Complex III, to a suspension of chloroplasts exposed to light. Would either $\mathbf{ATP}$or$\mathbf{NADPH}$ production be affected?

Short answer

Myxothiazol has an inhibiting effect on the production of $\mathrm{ATP}$and$\mathrm{NADPH}$.

Step-by-step solution

Similarity between the cytochrome and mitochondrial electron transport complex  

Cytochrome${\mathrm{b}}_6\mathrm{f}$ or plastoquinone-plastocyanin oxidoreductase is an enzyme present in the thylakoid membrane in chloroplasts of green algae, plants, and cyanobacteria. The electron transfer from plastoquinol to plastocyanin is catalyzed. Structurally and functionally chloroplast cytochrome ${\mathbf{b}}_{\mathbf{6}}\mathbf{f}$ is similar to mitochondrial complex III, while myxothiazol acts as an inhibitor of the mitochondrial electron transport in complex III.

Chain reaction due to interference of myxothiazol

As a result, myxothiazol is likely to interfere with electron transport (in the chloroplast). Because electron transport is obstructed, the Q cycle is interrupted, and no proton gradient is created. As a result, no$\mathrm{ATP}$ is produced, and electrons do not reach${\mathrm{NADP}}^{+}$.