Bioenergetics: Which of the following can uncouple electron transport from ATP synthesis in oxidative phosphorylation?

Introduction / Context:
Oxidative phosphorylation uses an electrochemical proton gradient (proton-motive force) to drive ATP synthesis via ATP synthase. Uncouplers dissipate this gradient or allow protons to return to the matrix independent of ATP synthesis, thereby uncoupling electron transport from phosphorylation.

Given Data / Assumptions:

• Fo is the membrane-embedded proton channel of ATP synthase; F1 is the catalytic head that synthesizes ATP.
• Dinitrophenol (DNP) is a classic protonophore that carries protons across the inner mitochondrial membrane.
• Uncoupling means electron transport continues while ATP synthesis drops due to the collapse of the gradient.

Concept / Approach:
Any process creating a proton leak lowers Δp (proton-motive force). A free proton channel (Fo without coupled F1 catalysis) or a mobile proton carrier (DNP) allows protons to re-enter the matrix independent of ATP formation. The respiratory chain then accelerates to maintain the gradient, increasing oxygen consumption while ATP yield falls.

Step-by-Step Solution:
Consider Fo alone: a proton-conducting pore uncouples by permitting proton flow without rotary catalysis.Consider DNP: shuttles protons across the membrane, short-circuiting the gradient.Both mechanisms dissipate Δp, so electron flow proceeds but phosphorylation efficiency collapses.

Verification / Alternative check:
Experimentally, DNP increases oxygen consumption while lowering ATP production. Genetic or chemical manipulations that open proton leak through Fo similarly elevate respiration with poor ATP yield.

Why Other Options Are Wrong:

• Neither (a) nor (b): False because both are established uncoupling mechanisms.
• Cytochrome c oxidase reduced: Part of the electron transport chain, not an uncoupler; it supports proton pumping rather than collapses the gradient.

Common Pitfalls:
Confusing inhibitors (e.g., oligomycin blocks Fo) with uncouplers (which open a leak). Inhibition lowers both oxygen consumption and ATP synthesis; uncoupling increases respiration but reduces ATP yield.

Final Answer:
Both (a) and (b).