Escherichia coli growing on glucose under anaerobic conditions at slightly alkaline pH carries out a mixed-acid fermentation resulting in the production of formate among the other products that can be excreted or further oxidized to H-2 and CO2. H-2 production is largely dependent on formate dehydrogenase H and hydrogenases 3 and 4 constituting two formate hydrogen lyases, and on the F0F1-ATPase. In this study, it has been shown that formate markedly increased ATPase activity in membrane vesicles. This activity was significantly (1.8-fold) stimulated by 100 mM K+ and inhibited by N,N'-dicyclohexylcarbodiimide and sodium azide. The increase in ATPase activity was absent in atp, trkA, and hyf but not in hyc mutants. ATPase activity was also markedly increased by formate when bacteria were fermenting glucose with external formate (30 mM) in the growth medium. However this activity was not stimulated by K+ and absent in atp and hyc but not in hyf mutants. The effects of formate on ATPase activity disappeared when cells were performing anaerobic (nitrate/nitrite) or aerobic respiration. These results suggest that the F0F1-ATPase activity is dependent on K+ uptake TrkA system and hydrogenase 4, and on hydrogenase 3 when cells are fermenting glucose in the absence and presence of external formate, respectively. (C) 2003 Elsevier Science (USA). All rights reserved.