2.B.3 The Nigericin (Nigericin) Family
Nigericin resembles monensin in being a monocarboxylate that catalyzes the electroneutral exchange of an alkali metal for H+ (antiport). However while monensin prefers Na+, nigericin prefers K+. At high K+ concentrations, nigericin can uncouple mitochondrial oxidative phosphorylation, suggesting that it may catalyze K+ uniport.
The generalized reaction (antiport) catalyzed by nigericin is:
K+ (out) + H+ (in) 
K+ (in) + H+ (out)