Proton-translocating ATPase function in bacteria Which statement best describes the activities catalyzed by the membrane-bound proton-translocating ATPase found in many bacteria?

Introduction / Context:
Energy transduction in bacteria often relies on a reversible, proton-translocating F1F0-ATPase embedded in the cytoplasmic membrane. Its directionality depends on cellular energetics and environmental conditions.

Given Data / Assumptions:

• The enzyme complex couples proton movement across the membrane with ATP synthesis/hydrolysis.
• Proton motive force (PMF) consists of a membrane potential and a transmembrane proton gradient.
• Cells can switch the enzyme’s direction depending on PMF and ATP availability.

Concept / Approach:
When the PMF is high (for example, during respiration), protons flow down their electrochemical gradient through the F0 sector, rotating the complex and driving ATP synthesis in F1. Under fermentative conditions or stress, cells may run the enzyme in reverse: ATP hydrolysis in F1 drives proton pumping via F0 to build PMF for solute transport and flagellar motility.

Step-by-Step Solution:
Define two modes: “synthase” mode (PMF → ATP) and “ATPase” mode (ATP → PMF).Recognize that many bacteria utilize both modes depending on metabolic state.Eliminate options that restrict the enzyme to only one direction or unrelated processes.Select the bidirectional description as most accurate.

Verification / Alternative check:
Experimental manipulations show reversal: collapsing PMF stimulates ATP hydrolysis and proton extrusion; providing PMF without ATP promotes ATP synthesis.

Why Other Options Are Wrong:

• A and B each capture only one possible direction and are therefore incomplete.
• C confuses transcription with energy transduction; RNA polymerase, not ATPase, makes mRNA.
• E contradicts the known rotary proton translocation mechanism.

Common Pitfalls:
Assuming “ATP synthase” and “ATPase” are different enzymes; they are the same complex operating in opposite directions.

Final Answer:
Can function in either direction, synthesizing ATP from proton influx or pumping protons by ATP hydrolysis