Studies of Hydrogenases

The size of the spin-spin interaction of the [NiFe] center and the [3Fe4S] cluster (S = Vi) is within the range that can be studied by pulse ELDOR spectroscopy. This PELDOR technique allows measurement of the spin-spin interaction and a determination of the effective distance between the two electron spins. Measurements have so far only been performed for D. vulgaris Miyazaki F hydrogenase [94] on the as-isolated enzyme (30% Ni-A and 70% Ni-B). The spin delocalization over the [3Fe4S] cluster had to be included for correct data analysis. Spin projection coefficients have been determined that indicate that the largest amount of eleetron spin density is located on the iron closest to the [NiFe] center. 

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Complementation with hypF gene from T. roseopersicina in a AhypF strain of R capsulatus was successful, a clear demonstration that a functionally active form of this Thiocapsa gene product is synthesised by the R capsulatus cells from the foreign template. The same experiment using a AhypF E. coli strain resulted in barely detectable complementation. We conclude that there must be strain dependent variations in the complementation capacity and that the most thoroughly studied bacterium, E. coli, may not be the best choice for such complementation studies of hydrogenase assembly and biosynthesis. 

It is likely that comparative structural and other studies of hydrogenases and nitrogenases will eventually illuminate events in the early evolution of energy-yielding mechanisms. We are indebted to the anaerobes for their necessary roles as recycling agents in Earth s element cycles. 

Hydrogen reduction Model studies of hydrogenase provide insights relevant to the pathogenic organism Helicobacter pylori and its ability to survive in the gastric mucosa. 

Concepts in Catalyst Design Based on Structural Studies of Hydrogenase Enzymes 167... 

Castro M, Cabral J (1989) Kinetic studies of hydrogenase in AOT reverse micelles. Enzyme Microb Technol 11(6-11)... 

As described herein, electrochemical studies of hydrogenases have been crucial in developing a mechanistic understanding of both the catalytic cycle of the enzyme and its oxidative inactivation. In turn, that understanding has been exploited in the constmetion of enzyme-based first-generation fuel cells and hydrogen production... 

A crystallographic analysis of xenon binding to [NiFe] hydrogenase, together with a molecular dynamic simulation study of xenon and dihydrogen diffusion in the enzyme interior, suggests the existence of hydrophobic channels connecting the molecular surface with the active site 184). 

Fe Q-band ENDOR study of the isotopically enriched Ni-C state of D. gigas and D. desulfuricans hydrogenases and Ni-B state of D. desulfuricans revealed a weak coupling between the Fe and the nickel atoms when the enzyme was in the Ni-A forms while no coupling was observed for the Ni-B form (186). A careful analysis of linewidth of Ni-A and Ni-B EPR signals detected in Fe enriched and nonenriched hydrogenase samples indicated that hyperfine interactions are lost in the spectral linewidth and, hence, nonde-tectable. 

Liu X, Ibrahim SK, Tard C, Pickett CJ. 2005. Iron-only hydrogenase Synthetic, structural and reactivity studies of model compounds. Coord Chem Rev 249 1641-1652. 

Amara, P., Volbeda, A., Fontecilla-Camps, J. C., Field, M. J., 1999, A Hybrid Density Functional Theory/Mo-lecular Mechanics Study of Nickel-Iron Hydrogenase Investigation of the Active Site Redox States , J. Am. Chem. Soc., 121, 4468. 

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