[The biochemistry, bioenergetics, and physiology of the CO-dependent growth of Rhodospirillum rubrum]

We have previously purified and characterized the holo and Ni-deficient forms of carbon monoxide dehydrogenase (CODH) from Rhodospirillum rubrum, developed protocols for insertion of various metals into the Ni site of the enzyme and characterized these metal substituted forms kinetically. In the current grant period a working hypothesis for the structure of the NiFeS center at the active site of CODH has been developed. A 22 kD FeS protein, which serves as the direct electron acceptor from CODH, has been identified and purified. This Fe[sub 4]S[sub 4] protein is required for anchoring CODH to the chromatophore membranes of R. rubrum and it is specifically required for reconstitution of CO-dependent H[sub 2] evolution in vitro. The R. rubrum genes for CODH, the 22 kD (ferredoxin-like) FeS protein, and the CO-induced hydrogenase have been isolated, sequenced, and mutagenized. This region has been designated the coo region with coos encoding CODH, cooF encoding the 22 kD ferredoxin and cooh the CO-induced hydrogenase. An ORF immediately downstream of cooS has been designated cooC. The cooS and cooF genes are cotranscribed, while cooH is on a separate transcript. The CO-dependent growth of R. rubrum has been established in the dark on medium containing only salts plus 0.2% yeast extract under an anaerobic CO gas phase. Under these conditions, R. rubrum grows with a doubling time of 5 hours, using CO as the sole energy source and the primary carbon source. The CO-induced hydrogenase activity from R. rubrum has been solubilized and partially purified. This hydrogenase is immunologically distinct from other hydrogenases. An in vitro system comprised of CODH, the 22 kD ferredoxin, hydrogenase and undefined factors has been reconstituted to give CO-dependent H[sub 2] evolution.