The number of accessible SH-groups in Escherichia coli membrane vesicles is increased by ATP or by formate

The number of accessible SH-groups was determined in membrane vesicles prepared from Escherichia coli growing in fermentation conditions at slightly alkaline pH on glucose with or without added formate. Addition of ATP or formate to the vesicles caused a ∼1.4-fold increase in the number of accessible SH-groups. The increase was inhibited by treatment with N-ethylmaleimide or the presence of the F₀F₁-ATPase inhibitors N,N^′-dicyclohexylcarbodiimide or sodium azide. The increase in accessible SH-groups was also absent in strains with the ATP synthase operon deleted or with the single F₀ domain cysteine Cysb21 changed to Ala. Using hyc and hyf mutants, it was shown that the increase was also largely dependent on hydrogenase 4 or hydrogenase 3, main components of formate hydrogen lyase, when bacteria were grown in the absence or presence of added formate. These results suggest a relationship between the F₀F₁-ATP synthase and hydrogenase 4 or hydrogenase 3 under fermentation conditions.