Biochemical and spectroscopic studies on Formate Dehydrogenase an enzyme isolated from the sulphate-reducing bacteria Desulfovibrio desulfuricans ATCC 27774.

M.G. RIVAS; P.J. GONZÁLEZ; C.D. BRONDINO; J.J.G. MOURA; I. MOURA

Münster (Germany)

Simposio; International Symposium on Microbial Sulfur Metabolism.; 2006

Anaerobic respiration with sulphate as terminal electron acceptor is a central component of the global sulphur cycle and is exhibited exclusively by prokaryotes. Sulphate reducing bacteria (SRB) are thus of major functional and numerical importance in many ecosystems like cyanobacterial microbial mats, marine sediments, oil fields environments, deep-sea hydrothermal vents and even in human diseases. SRB reduce a wide number of electron acceptors, including sulphate, sulphite, nitrate, nitrite within others; and various other organic compounds. The dissimilatory reduction of sulphate and nitrate in Desulfovibrio desulfuricans ATCC 27774 can function as the energyconserving process being coupled to the translocation of protons to the periplasm by using the quinone pool. However, other electron donors are produced during the lactate consumption in this organism, namely hydrogen and formate. The H2 is oxidized in the periplasm by the NiFe hydrogenase and the electrons are passed to the membrane quinol pool through a pathway that comprises the c3 and nine-haem cytochromes. The pathway of the electrons provided from the formate is still unknown. Currently, it is known that formate is oxidized to carbon dioxide by the heterotrimeric Formate dehydrogenase (Fdh). This enzyme is expressed when the culture is carried out with either sulphate or nitrate as final electron acceptor, and thus means that formate can serve as electron donor in both sulphate and nitrate respiration. Fdh isolated from the sulfate-reducing bacteria Desulfovibrio desulfuricans ATCC 27774 is a heterotrimeric enzyme (alpha, 92; beta, 29; and gamma, 16 kDa) that belongs to the DMSO reductase family of mononuclear Mo-containing. The catalytic subunit contains a Mo-bisMGD and one 4Fe-4S cluster, the beta subunit contain 3×[4Fe-4S] centers, and the gamma contain four c-type haems as redox cofactors [4]. EPR studies in both catalytic and inhibiting conditions, reveal distinct types of Mo(V) EPR active species. The involvement of this species in the reaction mechanism together with kinetic studies with alternative substrates and inhibitors will be presented.