Hydrogenase function

It is converted to coenzymes, nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate (NADP). These coenzymes are bound to hydrogenases, function as oxidants by accepting hydrogen and electrons from substrates and become reduced. 

Balk J, Pierik AJ, Aguilar Netz DJ, Miihlenhoff U, Lill R (2005) Narlp, a conserved eukaryotic protein with similarity to Fe-only hydrogenases, functions in cytosolic iron-sulphur protein biogenesis. Biochem Soc Trans 33 86-89 Barton RM, Worman HJ (1999) Prenylated prelamin A interacts with Narf, a novel nuclear protein. J Biol Chem 274 30008-30018... 

Kubas GJ. Fundamentals of H2 binding and reactivity on transition metals underlying hydrogenase function and H2 production and storage. Chem Rev 2007 107 4152-205. 

Pandelia ME, Ogata H, Lubitz W. Intermediates in the catalytic cycle of [NiFe] hydrogenase functional spectroscopy of the active site. ChemPhysChem. 2010 11(6) 1127-40. 

Frenking G, Cremer D (1990) The Chemistry of the Nobles Gas Elements Helium, Neon, and Argon - Experimental Facts and Theoretical Predictions. 73 17-96 Frey M (1998) Nickel-Iron Hydrogenases Structural and Functional Properties. 90 97-126 Fricke B (1975) Superheavy Elements. 21 89-144... 

Functional proteins are also involved in high-affinity Ni transport for hydrogenase synthesis. One example is the nikABCDE gene cluster of Escherichia coli 20). NikA is a periplasmic Ni-binding protein. 

Midpoint potential values are useful quantitites for defining the role of the various centers in the system. In some instances, these values have even been used to predict the location of the centers in the electron transfer chain, assuming that the potential increases along the chain from the electron donor to the electron acceptor. In several oxidoreductases, however, the measured potential of some centers was found to be clearly outside the range defined by the donor and the acceptor, which raised an intriguing question as to their function. This was observed, for instance, in the case of the [4Fe-4S] (Eni = -320 mV) center in E. coli fumarate reductase (249), the [3Fe-4S] + (Era = -30 mV) center in D. gigas hydrogenase (207), and the low-potential [4Fe-4S] + + (E, = 200 and -400 mV) centers in E. 

Fontecilla-Camps JC, Volheda A, CavazzaC, NicoletY. 2007. Structure/function relationships of [NiFe]- and [FeFe]-hydrogenases. Chem Rev 107 4273-4303. 

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. 

Biomimetic chemistry of nickel was extensively reviewed.1847,1848 Elaborate complexes have been developed in order to model structural and spectroscopic properties as well as the catalytic function of the biological sites. Biomimetic systems for urease are described in Section 6.3.4.12.7, and model systems for [Ni,Fe]-hydrogenases are collected in Section 6.3.4.12.5. 

Before going on to describe the functions of the metals we observe that among heavier non-metals only selenium, chlorine and other halogens need any further comment. Selenium is found in some hydrogenases in even the most primitive life forms and may be it was required initially since it is a more effective catalytic centre than sulfur although much less available. (Compare tungsten with molybdenum later.) Its amino acid selenomethionine is coded in early DNA Later it is involved... 

Fig. 5.7. In green sulfur bacteria and in some archaebacteria, a reverse citric acid cycle is used for the assimilation of C02. It must be assumed that this was the original function of the citric acid cycle that only secondarily took over the role as a dissimulatory and oxidative process for the degradation of organic matter. A major enzyme here is 2-oxoglutarate ferredoxin for C02 fixation. Note that it, like several other enzymes in the cycle, uses Fe/S proteins. One is the initial so-called complex I which has eight different Fe/S centres of different kinds but no haem (see also other early electron-transfer chains, e.g. in hydrogenases).

Figure 2 Structures of the actrive sites of metalloenzymes containing metal-sulfur cluster units, (a) Fe only hydrogenase, H-cluster (Hoxfarm) (b) Sulfite reductase (c) NiFe carbon monoxide dehydrogenase, C-cluster and (d) NiFe carbon monoxide dehydrogenase, A-cluster, which functions as acetyl-CoA synthase...

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