Non-haem iron proteins

Figure 25.9 Some non-haem iron proteins (a) rubredoxin in which the single Fe is coordinated, almost tetra-hedrally, to 4 cysteine-sulfurs, (b) plant ferredoxin, [Fe2S2(S-Cys)4], (c) [Fe4S4(S-Cys)4] cube of bacterial ferredoxins. (This is in fact distorted, the Fe4 and S4 making up the two interpenetrating tetrahedra, of which the latter is larger than the former).

Rubrerythrin is the trivial name given to a family of non-haem iron proteins that have been isolated from a number of bacteria (Figure 6.2). The structure of the best characterized rubrerythrin, that from Desulfovibrio vulgaris, has been determined by... 

Fig. 3. Cyclic reduction and oxidation of cytochrome P-450 in adrenal cortical mitochondria. FP. adrenodoxin reductase non-haem iron protein, adrenodoxin SH, substrate SOH. hydroxylated product (from Ref. 24, with permission).

There are no reported optical spectra attributed to FeIV in non-haem iron proteins suggested to have ferryl intermediates. However, a low-intensity peak at about 600 nm is observed in a model non-haem ferryl compound generated by the addition of H202to a (p-oxo) diferric complex [130],... 

Lipid hydroperoxides are fairly stable molecules under physiological conditions, but their decomposition is catalysed by transition metals and metal complexes (O Brien, 1969). Both iron(II) and iron(III) are effective catalysts for hydroperoxide degradation, but the former is more so (Halliwell and Gutteridge, 1984). These include complexes of iron salts with low molecular weight chelates, non-haem iron proteins, free haem, haemoglobin, myoglobin. 

In liver, muscle and other tissues iron is taken up by the cells when transferrin saturation levels are high and deposited first in ferritin and subsequently transferred to haemosiderin. This pool of ferritin iron is most likely used within these cells to meet requirements for synthesis of haem enzymes, myoglobin and other non-haem iron proteins. The ferritin can also store iron released from the breakdown of such iron containing proteins in the course of their turnover. Mobilisation of iron from these tissues once again probably involves reduction of iron to Fe2+ and its transfer across the cell membrane to transferrin. In such tissues the level of transferrin saturation seems likely to play a major role in determining the balance between deposition of iron in ferritin and its mobilization from the storage form. 

It has recently become apparent that iron-sulphur, or non-haem iron, proteins occur widely in animals, plants, and bacteria, and that they play a very important role in such functions as respiration, photosynthesis, and nitrogen-fixation. Both iron-sulphur proteins and cytochromes are electron carriers containing iron, but their active centres are entirely different. Hall and Evans have recently reviewed iron-sulphur proteins, and a discussion on nitrogen fixation held in June 1968 has also been published. ... 

Hemerythrin is a non-haem iron protein which transports oxygen in a few simple invertebrates. The nature of the binding of the oxygen to the iron, and of the iron to the protein, is not fully understood, although the presence of histidine and tyrosine at the active site has recently been demonstrated. Magnetic and spectroscopic data have been used to obtain information about the oxidation states of the two iron atoms at the active site in the oxygenated and oxygen-free proteins. 

One of the simplest of the non-haem iron proteins is the rubredoxin from Clostridium pasteurianum, which contains one iron atom per molecule and undergoes a reversible one-electron oxidation and reduction. The... 

A possible model for the chromophore of non-haem iron proteins has been described which contains 2-mercaptoethanol, but the rate of uptake of oxygen by the model is higher than would be expected on the basis of a simple reduction of Fe " to Fe" by the mercaptoethanol followed by its reoxidation to Fe" . A rather looser model is mercaptoacetato-bis(ethylenediamine)cobalt(iii). The kinetics of the inner-sphere reduction of this and its oxygen analogue by Cr" have been reported. The rate constant (25 °C, ionic strength = OT) for [Co enaCSCHaCOa)] is > 2 X 10 lmol-is-i, and that for [Co en2(OCH2COa)]+ is 9-9 x lOM mol s . ... 

The o>-hydroxylase system (alkane 1-mono-oxygenase, EC 1.14.15.3) has non-haem irons as, apparently, the only prosthetic groups directly involved in the hydroxylation reactions. The system from Pseudomonas oleovorans has been isolated by Coon and co-workers (Kusunose et aL, 1964). The system was fractionated into three components a non-haem iron protein (similar to the rubredoxins), a flavoprotein and a final component required for hydroxylase activity called the cy-hydroxylase. The... 

Electron carriers which contain iron (and in the case of cytochrome oxidase also copper) they undergo oxidation and reduction by electron transfer alone. These are the cytochromes, in which the iron is present in a haem molecule, and nonhaem iron proteins, sometimes called iron—sulphur proteins, because the iron is bound to the protein through the sulphur of the amino acid cysteine. Figure 3.19 shows the arrangement of the iron in non-haem iron proteins and the three different types of haem that occur in cytochromes ... 

There are two steps in which a hydrogen carrier reduces an electron carrier the reaction between the flavin and non-haem iron protein in complex I and the reaction between ubiquinol and cytochrome b plus a non-haem iron protein in complex II. 

The reaction between non-haem iron protein and ubiquinone in complex I is the reverse — a hydrogen carrier is reduced by an electron carrier. 

Zhou NY, Jenkins A, Chion C, Leak DJ. 1998. The alkene monooxygenase from Aon-thobacter Vy2 is a binuclear non-haem iron protein closely related to toluene 4-monooxygenase. FEBS Lett 430 181-185. 

X 10 s 38 = 1.8 X 10 s. Even in the absence of cooperative phenomena, 08 binding by hemocyanin involves a minimum of two elementary steps, and this finding might be correlated with the presence of two metal atoms in each site. Raman spectroscopy has been used to investigate the nature of the co-ordination of iron in clostridial rubredoxin, and e.s.r. and Mossbauer spectroscopy have been used to study the non-haem iron proteins cysteamine oxygenase and adrenodoxin. ... 

The key issue for RR spectroscopists dealing with non-haem iron proteins is to determine the geometry of the oxygen-bridged binuclear complexes as well as to identify the nature of the ligands. In these studies, the RR spectra of i 0-labelled samples significantly supports the interpretation. 

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