Nickel cofactors

Cheesman MR, Ankel Fuchs D, Thauer RK and Thompson AJ (1989) The magnetic properties of the nickel cofactor F430 in the enzyme methyl-coenzyme M reductase of Methanobacterium ther-moautotrophicum. Biochem J 260 613—616. 

No nickel-requiring enzymes or proteins are known in vertebrates, although biological roles of nickel enzymes and cofactors have been found in plants and bacteria. Although the role of nickel in human physiology has not been confirmed directly, the evidence strongly suggests that nickel is required by humans [263],... 

The next five transition metals iron, cobalt, nickel, copper and zinc are of undisputed importance in the living world, as we know it. The multiple roles that iron can play will be presented in more detail later in Chapter 13, but we can already point out that, with very few exceptions, iron is essential for almost all living organisms, most probably because of its role in forming the amino acid radicals required for the conversion of ribonucleotides to deoxyribonucleotides in the Fe-dependent ribonucleotide reductases. In those organisms, such as Lactobacilli6, which do not have access to iron, their ribonucleotide reductases use a cobalt-based cofactor, related to vitamin B12. Cobalt is also used in a number of other enzymes, some of which catalyse complex isomerization reactions. Like cobalt, nickel appears to be much more extensively utilized by anaerobic bacteria, in reactions involving chemicals such as CH4, CO and H2, the metabolism of which was important... 

This enzyme [EC 1.2.99.2], also known as acetyl-CoA synthase, catalyzes the reaction of carbon monoxide with water and an acceptor to produce carbon dioxide and the reduced acceptor. The cofactors of this enzyme include nickel and zinc ions as well as non-heme iron. Methyl viologen can act as the acceptor substrate. The enzyme is isolated from Clostridium sp. Interestingly, it also catalyzes an exchange reaction of carbon between Cl of acetyl-CoA and carbon monoxide. The protein participates in the synthesis of acetyl-CoA from carbon dioxide and hydrogen in the organisms. 

Corphin is the F-430 cofactor found in methyl-coenzyme M reductase, a nickel-containing enzyme that participates in the conversion of carbon dioxide to methane in methanogenic bacteria. The nickel ion in F-430 is coordinated by the tetrahydrocorphin ligand, which contains structural elements of both porphyrins and corrins. 

A tetrapyrrole (related to porphyrins and corrins) containing a nickel ion. This cofactor, corphin, is a crucial component of methyl-coenzyme M reductase, a bacterial enzyme participating in the formation of methane. 

More complex assemblies of iron and sulfur, sometimes extended to other metals like nickel, molybdenum, vanadium, or other iron centers are found in some enzymes, that catalyze the transformation of small molecules [1, 14]. Among these centers, we will focus next on the P cluster and the FeMo cofactor of nitrogenase and on the H cluster of the iron-only hydrogenase. 

The acetogenic bacterium Moorella thermoacetica contains a cofactor comprising iron, sulfur, copper and nickel in the enzyme carbon monoxide dehyd-rogenase/acetyl-CoA, and Drennan et al. proposed a new role for Cu in biology on the basis of their structure determination at 2.2 A resolution.81 The Cu bridges the Fe4S4 cluster and Ni centre via three p2-S atoms, and hence the reported EPR... 

To accomplish these reactions a surprising variety of specialized cofactors are needed.351 352 434 The first of these, coenzyme M, 2-mercaptoethane sulfonate, was discovered in 1974.436 It is the simplest known coenzyme. Later, the previously described 5-deazaflavin F420 (Section B), a nickel tetrapyrrole F430 (Chapter 16), methanopterin (Fig. 

Nickel is found in at least four enzymes urease, certain hydrogenases, methyl-CoM reductase (in its cofactor F430) of methanogenic bacteria, and carbon monoxide dehydrogenase of acetogenic and methanogenic bacteria 434... 

It is not known at present if the nickel is coordinated directly to the protein, as in copper and iron-sulfur proteins, or to an organic cofactor, as in the molybdenum hydroxylases and hemoproteins. 

An enzyme cofactor can be either an inorganic ion (usually a metal cation) or a small organic molecule called a coenzyme. In fact, the requirement of many enzymes for metal-ion cofactors is the main reason behind our dietary need for trace minerals. Iron, zinc, copper, manganese, molybdenum, cobalt, nickel, and selenium are all essential trace elements that function as enzyme cofactors. A large number of different organic molecules also serve as coenzymes. Often, although not always, the coenzyme is a vitamin. Thiamine (vitamin Bj), for example, is a coenzyme required in the metabolism of carbohydrates. 

Hydration and/or dehydration reactions are frequently catalyzed by metallopro-teins. Examples are proteins containing nickel (urease), zinc (e.g., peptidases), molybdenum (the hydratase partial reaction of formate oxidoreductase), tungsten (acetylene hydratase). An obvious difference between Ni, Zn, on the one hand, and Fe, Mo, W, on the other, is that the first are directly coordinated to the protein whereas the latter are also part of a cofactor. With reference to the Fe/S cluster in aconitase it has been suggested that cofactor coordination may provide an added flexibility to the active site, in particular to the substrate binding domain [15],... 

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