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Abstract

Two hydrogenases, differing in their specificity for the electron carrier F420, were present in cell-free extracts of Methanobacterium formicicum. The two hydrogenases were resolved either by gel filtration, ion-exchange chromatography, ro by electrophoresis in polyacrylamide gel. The larger hydrogenase (designated the F420-reactive hydrogenase) showed factor F420-linked and methyl viologen-linked activities; two forms (Mr 600 000 and 380 000) were obtained from M. formicicum strain MF. The smaller enzyme (designated F420-non-reactive hydrogenase; Mr 70 000 from M. formicicum strain MF) showed only methyl viologen-linked activity. The F420-reactive hydrogenase contained subunits of Mr 42 600, 34 000 and 23 500. The F420-non-reactive hydrogenase contained subunits of Mr 48 000 and 38 000. The subunit patterns and the results of peptide mapping indicate that F420-reactive and F420-non-reactive hydrogenases are distinct enzymes. The F420-reactive hydrogenase was more stable under aerobic conditions, and both hydrogenases could be purified in air. The aerobically prepared enzymes must be incubated with a reducing agent to become active. After activation, the F420-reactive hydrogenase became unstable at 25–30°C but was stable at 0–5°C. Besides the major F420-non-reactive hydrogenase, a minor F420-non-reactive hydrogenase (Mr 145 000) was also observed in extracts of M. formicicum. The hydrogenases of M. formicicum strains MF and JF were very similar. In M. bryantii, several hydrogenase species with different electrophoretic mobilities were observed, but their properties different from those of the M. formicicum enzymes.