Nickel superoxide dismutase enzymes

In contrast to the abundance of Fe-proteins, there are only six known nickel-containing enzymes hydrogenase, CO dehydrogenase (CODA), acetyl-CoA synthase (ACS), superoxide dismutase, urease, and S-methyl-CoM methylreductase. Among these enzymes, it exists in very diverse environments, including a dinickel site (urease), a Ni-Fe heterobinuclear site (hydrogenase), a Ni-Fe4S4 heterometallic... 

Superoxide dismutases may contain a range of metals Mn, Fe, or both Cu and Zn, and representatives of all these are found in prokaryotes. The nickel enzyme is noted later. 

Nickel is found in thiolate/sulflde environment in the [NiFe]-hydrogenases and in CODH/ACS.33 In addition, either a mononuclear Ni-thiolate site or a dinuclear cysteine-S bridged structure are assumed plausible for the new class of Ni-containing superoxide dismutases, NiSOD (A).34 [NiFe]-hydrogenase catalyzes the two-electron redox chemistry of dihydrogen. Several crystal structures of [NiFe]-hydrogenases have demonstrated that the active site of the enzyme consists of a heterodinuclear Ni—Fe unit bound to thiolate sulfurs of cysteine residues with a Ni—Fe distance below 3 A (4) 35-39 This heterodinuclear active site has been the target of extensive model studies, which are summarized in Section 6.3.4.12.5. 

A newly discovered nickel enzyme is superoxide dismutase (SOD) from the acti-nomycete Streptomyces sp [164,165]. In its protein properties, this enzyme is... 

Superoxide dismutase (SOD) catalyzes the disproportionation of superoxide to peroxide and oxygen according to equation (2). Four different types of SOD are known, containing either Cu and Zn see Copper Proteins with Type 2 Sites), Fe, Mn, or Ni see Nickel Enzymes Cofactors). The Fe and Mn containing SODs have very similar structures and can be further subdivided into metal-specific (i.e. functioning only when the correct metal is bound) and cambialistic (functioning with either Fe or Mn bound to the active site). 

The nickel enzymes covered in this article can be divided into two groups redox enzymes and hydrolases. The five Ni redox enzymes are hydrogenase, CO dehydrogenase (CODH), acetyl-CoA synthase (ACS), methyl-Coenzyme M reductase (MCR), and superoxide dismutase (SOD). Glyoxalase-I and urease are Ni hydrolases. Ni proteins that are not enzymes are not covered, because they have been recently reviewed. These include regulatory proteins (NikR) and chaperonins and metal uptake proteins (CooJ, CooE, UreE, and ABC transporters). A recent crystal structure of NikR, shown in Figure l(i), is a notable recent achievement in this area. ... 

Superoxide dismutase, more commonly called SOD, is an unusual enzyme that breaks down even the most destructive free radicals in the body. At least four different types of it are now known, involving five different trace elements as parts of the molecular structure. Those metals are iron, manganese, nickel, and, in one form of the enzyme, a combination of copper and zinc. Others may be discovered in the future. The SOD enzyme especially protects the nucleic acids of cells from attack by free radicals. This is very important because DNA damage is one way that cancer can develop in the body. 

Nickel and molybdenum, like iron, play important roles in nitrogen assimilation. Nickel occurs in the enzyme urease, and thus is required by phytoplankton grown on urea as a nitrogen source. It also occurs in Ni-superoxide dismutase found in many marine cyanobacteria, which, like the Mn and Fe forms of the enzyme, removes harmful superoxide radicals from cells. Little is currently known about the potential for nickel limitation in the ocean. 

Previous sections focused on the enzymatic determination of NO, N02 using copper, zinc superoxide dismutase (SODl), and NOs using nitrate reductase (NaR)-modified Pt electrodes. This is a costly, time-consuming, and tedious procedure and the enzymes are not very stable. In order to resolve these drawbacks, the highly stable metaUoporphyrin-modified electrode would be the preeminent choice for the determination of NO metaboHtes. Different metalloporphyrins including nickel, iron, cobalt, manganese, and some other metal complexes were previously used for the... 

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