Uncoupling agents distinguish between the effects of metabolic inhibitors and transport inhibitors.

In studies with toad bladders, the uncoupling agent 2,4-dinitrophenol (DNP) reversed the inhibition of CO2 production produced by direct inhibition of transport. In contrast, DNP did not reverse the inhibition of CO2 production brought about by metabolic inhibitors. Therefore, the response to DNP distinguished between inhibition of transport and metabolism; this approach may be useful for the investigation of factors that regulate active transport.