Next, transport activity observed when vesicles are treated with the weak acid protonophore carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) reveals the transporter's ability to perform anion uniport (Figure ). The protonophore facilitates efficient proton transport, which removes the rate-limiting proton transport step. Although slightly less efficient than FCCP, a similar protonophore, carbonyl cyanide-mchlorophenylhydrazone (CCCP), may be used in place of FCCP as a cheaper alternative.