Effect of redox potential on activity of hydrogenase 1 and hydrogenase 2 in Escherichia coli

Abstract.

This report elucidates the distinctions of redox properties between two uptake hydrogenases in Escherichia coli. Hydrogen uptake in the presence of mediators with different redox potential was studied in cell-free extracts of E. coli mutants HDK103 and HDK203 synthesizing hydrogenase 2 or hydrogenase 1, respectively. Both hydrogenases mediated H₂ uptake in the presence of high-potential acceptors (ferricyanide and phenazine methosulfate). H₂ uptake in the presence of low-potential acceptors (methyl and benzyl viologen) was mediated mainly by hydrogenase 2. To explore the dependence of hydrogen consumption on redox potential of media in cell-free extracts, a chamber with hydrogen and redox (E _h) electrodes was used. The mutants HDK103 and HDK203 exhibited significant distinctions in their redox behavior. During the redox titration, maximal hydrogenase 2 activity was observed at the E _h below –80 mV. Hydrogenase 1 had maximum activity in the E _h range from +30 mV to +110 mV. Unlike hydrogenase 2, the activated hydrogenase 1 retained activity after a fast shift of redox potential up to +500 mV by ferricyanide titration and was more tolerant to O₂. Thus, two hydrogenases in E. coli are complementary in their redox properties, hydrogenase 1 functioning at higher redox potentials and/or at higher O₂ concentrations than hydrogenase 2.