Effects of Ellman’s reagent and other thiol compounds on ion transport and ATPase activity in anaerobically grown Escherichia coli cells

It was found that modification of thiol (SH-) groups of membrane proteins by Ellman’s reagent (5,5′-dithiol-bis-(2-nitrobenzoic) acid) results in inhibition of proton efflux and K + influx in anaerobically grown (pH 7.5) wild-type strains of Escherichia coli and causes disturbances in K + -dependent, N,N′-dicyclohexylcarbodiimide-sensitive ATPase activity and molecular hydrogen production. No such effects were observed after substitution of the cysteine residue in the b-subunit of F 0 of proton F 0 F 1 -ATPase for alanine. Moreover, the redox potential (RP) decreased as a result of H 2 release during glucose fermentation and formate utilization was partly restored in the presence of Ellman’s reagent. Similar changes were established when another specific SH-reagent, succinimidyl-6(β-maleimidopropionamido)hexanoate, was used. Another thiol reagent, N-ethylmaleimide, did not exert such effects despite its inhibitory action on ion transport and ATPase activity. The data obtained provide conclusive evidence in favor of essential role of thiol groups and the cysteine residue in the b-subunit of F 0 of F 0 F 1 -ATPase in proton-potassium exchange and H 2 production in E. coli cells. The results also point to a possible involvement of SH-groups in the TrkA system of K + uptake and an involvement of hydrogenases 3 or 4 in the interactions of these integral proteins with each other.