Metalloproteins, redox reactions

Metalloprotein redox reactions. (L. E. Bennett, Progr. Inorg. Chem., 1973, 18, 1). Novel metalloporphyrins-synthesis and implications. (D. Ostfield and M. Tsutsui, Accounts Chem. Res., 1974, 7, 52). 

Metalloprotein Redox Reactions , L. E. Bennett, Progr. Inorg. Chem., 1973, 18, 1. 

Within a given metalloprotein, redox reactions involving two electrons which effectively convert a ferredoxin into HIPIP do not occur. 

The two species represented in eq. 29.13 do not actually possess localized Fe(ll) and Fe(lll) centres, rather the electrons are delocalized over the cluster core. One could envisage further oxidation to species that are formally 3Fe(lll) Fe(ll) and 4Fe(lll). Whereas the latter is never accessed under physiological conditions, 3Fe(lll) Fe(ll) is the oxidized form of HIPIP (high-potential protein). Thus, 2Fe(lll) -2Fe(ll) is the reduced form of HIPIP or the oxidized form of ferredoxin. In contrast to the reduction potentials of ferredoxins, those of HIPIPs are positive, e.g. 4-360 mV for HIPIP isolated from the bacterium Chromatium vinosum. Within a given metalloprotein, redox reactions involving two electrons which effectively convert a ferredoxin into HIPIP do not occur. 

If metalloprotein redox reactions obey Marcus theory, the ratio of the rate of oxidation of reduced protein by [Co(ox)3] and [Co(phen)3], R = i2[co(phen)3]3+/ i2[co(ox)3]3-, should be a constant, independent of the protein. Under conditions where protein-oxidant preassociation is minimized, R values increase in the order... 

Redox reactions of sulphur-containing amino-acid residues in proteins and metalloproteins. 

Some of the critical enzymes in our cells are metalloproteins, large organic molecules made up of folded polymerized chains of amino acids that also include at least one metal atom. These metalloproteins are intensely studied by biochemists, because they control life and protect against disease. They have also been used to trace evolutionary paths. The d-block metals catalyze redox reactions, form components of membrane, muscle, skin, and bone, catalyze acid-base reactions, control the flow of energy and oxygen, and carry out nitrogen fixation. 

Weser U (1985) Redox Reactions of Sulphur-Containing Amino-Acid Residues in Proteins and Metalloproteins, an XPS Study. 61 145-160 Weser U (1973) Structural Aspects and Biochemical Function of Erythrocuprein. 17 1-65 Weser U, see Abolmaali B (1998) 91 91-190... 

The many redox reactions that take place within a cell make use of metalloproteins with a wide range of electron transfer potentials. To name just a few of their functions, these proteins play key roles in respiration, photosynthesis, and nitrogen fixation. Some of them simply shuttle electrons to or from enzymes that require electron transfer as part of their catalytic activity. In many other cases, a complex enzyme may incorporate its own electron transfer centers. There are three general categories of transition metal redox centers cytochromes, blue copper proteins, and iron-sulfur proteins. 

Fedurco M. 2000. Redox reactions of heme-containing metalloproteins Dynamic effects of self-assemhled monolayers on thermod3mamics and kinetics of c)dochrome c electron-transfer reactions. Coord Chem Rev 209 263-331. 

The substitution process permeates the whole realm of coordination chemistry. It is frequently the first step in a redox reaction and in the dimerization or polymerization of a metal ion, the details of which in many cases are still rather scanty (e.g. for Cr(III) ). An understanding of the kinetics of substitution can be important for defining the best conditions for a preparative or analytical procedure. Substitution pervades the behavior of metal or metal-activated enzymes. The production of apoprotein (demetalloprotein and the regeneration of the protein, as well as the interaction of substrates and inhibitors with metalloproteins are important examples. ... 

Redox reactions usually lead, however, to a marked change in the species, as reactions 4-6 indicate. Important reactions involve the oxidation of organic and metalloprotein substrates (reactions 5 and 6) by oxidizing complex ions. Here the substrate often has ligand properties, and the first step in the overall process appears to be complex formation between the metal and substrate species. Redox reactions will often then be phenomenologically associated with substitution. After complex formation, the redox reaction can occur in a variety of ways, of which a direct intramolecular electron transfer within the adduct is the most obvious. 

Mauk, A. G., Scott, R. A., and Gray, H. B. (1980). Distances of electron transfer to and from metalloprotein redox sites in reactions with inorganic complexes. J. Am. Chem. Soc. 102,4360-4363. 

Redox Reactions of Sulphur-Containing Amino-Acid Residues in Proteins and Metalloproteins, an XPS Study... 

Metal bridges are formed from enzymes or hormones to the substrates. These intermediate complexes are able to enhance the reaction in a number of metabolic processes, 3. Some metal ions are known to act as a cofactor or coenzyme being involved in redox reactions directly. Further, metalloproteins may serve as a pool for metal storage. Examples for this are displayed by ferritin, transferrin or ferrichrome, to mention just a few. 

The biological catalytic activity of metalloproteins for redox reactions is usually associated with a particular coordination environment of the metal active site [160, 161], In particular, there has been considerable interest in 02-binding and -activation by non-heme metalloenzymes [162-167). A redox-active metal center is often associated with another metal center which can accelerate the redox process of O2... 

Experimental investigation of the factors that control the rates of biological redox reactions has not come as far as the study of the electron transfers of metal complexes, because many more variables must be dealt with (e.g., asymmetric surface charge, nonspherical shape, uncertain details of structures of proteins complexed with small molecules or other proteins). Many experimental approaches have been pursued, including the covalent attachment of redox reagents to the surfaces of metalloproteins. 

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