Purification of the membrane-bound hydrogenase of Escherichia coli

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Abstract
The membrane-bound hydrogenase (EC 1.12.-) of aerobically grown E. coli cells was solubilized by treatment with deoxycholate and pancreatin. The enzyme was further purified to electrophoretic homogeneity by chromatographic methods, including hydrophobic-interaction chromatography, with a yield of 10% as judged by activity and an overall purification of 2140-fold. The hydrogenase was a dimer of identical subunits with a MW of 113,000 and contained 12 Fe and 12 acid-labile S atoms/molecule. The .epsilon.400 was 49,000 M-1 .cntdot. cm-1. The hydrogenase catalyzed both H2 evolution and H2 uptake with a variety of artificial electron carriers, but would not interact with flavodoxin, ferredoxin or nicotinamide and flavin nucleotides. No physiological electron carrier for the hydrogenase was identified. With methyl viologen as the electron carrier, the pH optimum for H2 evolution and H2 uptake was 6.5 and 8.5, respectively. The enzyme was stable for long periods at neutral pH, low temperatures and under anaerobic conditions. The half-life of the hydrogenase under air at room temperature was .apprx. 12 h, but it could be stabilized by methyl viologen and benzyl viologen, both of which are electron carriers for the enzyme, and by bovine serum albumin. The hydrogenase was strongly inhibited by CO (Ki [inhibition constant] = 1870 Pa), heavy-metal salts and high concentrations of buffers, but was resistant to inhibition by thiol-blocking and metal-complexing reagents. These aerobically grown E. coli cells lacked formate hydrogenlyase activity and cytochrome c552.

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