SUMMARY: Two mutant strains of , AKl 1 and AK22, express normal levels of hydrogenase activity, assayed by deuterium exchange, when grown on glucose or complex medium but cannot reduce methyl viologen by H nor grow on fumarate plus H. The mutant strains also lack formate hydrogenlyase and formate dehydrogenase activities. The mutation in these strains was located near minute 17 of the genome map and a single mutation was shown to be responsible for loss of both hydrogen uptake and formate-related activities. Membrane vesicles and solubilized membranes of strains AK11 and AK22 were capable of methyl viologen reduction by H2 and had the normal complement of hydrogenase isoenzymes 1 and 2. Intact cells of the mutant strains could reduce fumarate by H but could not grow under these conditions. A plasmid, pAKl1, was isolated, as well as smaller plasmids derived from it, which restored the hydrogen uptake activities in the two mutant strains, the smallest active DNA fragment being 1.4 kb. The formate activities were partially restored by some of the plasmids. The plasmids which restored hydrogen uptake activities led to synthesis of a polypeptide of subunit molecular mass 30 kDa.


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