Ferredoxins electronic properties

The resonance Raman spectrum of this complex bears a close resemblance to that of the D. gigas ferredoxin II. Since the vibrational bands responsible for the resonance Raman spectrum are not strongly dependent on the electronic properties, it is not surprising that an analogue with a different metal can be identified using this technique. 

In this work we examine the low energy UV-visible absorption spectrum of the [Fe2 ft - S2) P o- 61148) )2] complex, Figure 1, whose synthesis, structure, and properties have recently been reported. The complex contains a [Fe — S — S - Fe] core and is a structural isomer of the 2-Fe [Fe — ill — 8)2 — Fe ferredoxin. The electronic structure of the disulfide complex is, however, unknown, and can be associated with either an antifer-romagnetically (AF) coupled [Fe d ) - - Fe d )] system, or with a... 

The subunits of CODH/ACS have been isolated (see earlier discussion). The isolated a subunit contains one Ni and four Fe and has spectroscopic properties (186) similar to those of Cluster A, the active site of acetyl-CoA synthesis (212). Unfortunately, it has no ACS activity. Therefore, ACS activity may reside in the a subunit or it may require both the a and the fi subunits. If Clusters B and/or C of the B subunit are involved in acetyl-CoA synthesis, one possible role could be in electron transfer. Although acetyl-CoA synthesis and the CO/ exchange reactions do not involve net electron transfer, both of these reactions are stimulated by ferredoxin, indicating that internal electron transfer within CODH/ACS may be required during the reaction (121). Further studies with the isolated subunits and the reconstitu-... 

In particular, the study of SRB ferredoxins enables us to survey the different properties of simple iron-sulfur proteins, including electron transfer, flexibility in coordination chemistry, and ability to undergo cluster interconversions. Most of the observations can be extrapolated to more complex situations. 

For the cytochrome c-plastocyanin complex, the kinetic effects of cross-linking are much more drastic while the rate of the intracomplex transfer is equal to 1000 s in the noncovalent complex where the iron-to-copper distance is expected to be about 18 A, it is estimated to be lower than 0.2 s in the corresponding covalent complex [155]. This result is all the more remarkable in that the spectroscopic and thermodynamic properties of the two redox centers appear weakly affected by the cross-linking process, and suggests that an essential segment of the electron transfer path has been lost in the covalent complex. Another system in which such conformational effects could be studied is the physiological complex between tetraheme cytochrome and ferredoxin I from Desulfovibrio desulfuricans Norway the spectral and redox properties of the hemes and of the iron-sulfur cluster are found essentially identical in the covalent and noncovalent complexes and an intracomplex transfer, whose rate has not yet been measured, takes place in the covalent species [156]. 

The biological functions of chloroplast ferredoxins are to mediate electron transport in the photosynthetic reaction. These ferredoxins receive electrons from light-excited chlorophyll, and reduce NADP in the presence of ferredoxin-NADPH reductase (23). Another function of chloroplast ferredoxins is the formation oT" ATP in oxygen-evolving noncyclic photophosphorylation (24). With respect to the photoreduction of NADP, it is known that microbial ferredoxins from C. pasteurianum (16) are capable of replacing the spinach ferredoxin, indicating the functional similarities of ferredoxins from completely different sources. The functions of chloroplast ferredoxins in photosynthesis and the properties of these ferredoxin proteins have been reviewed in detail by Orme-Johnson (2), Buchanan and Arnon (3), Bishop (25), and Yocum et al. ( ). 

The general properties of simple electron transfer proteins (e.g., the ferredoxins, the blue, or type 1, copper proteins, cytochrome c, and... 

One of the earliest recognized Fe S proteins was that associated with mitochondrial electron transport (Rieske et al., 1964). Even in the first partial in vivo characterization it was apparent that the protein had spectral properties that set it apart from the bacterial and plant-type ferredoxins which had just been discovered. Namely, the EPR spectrum had a gave near 1.91 and the high-held g value was shifted upheld. Furthermore, the protein had an Eq of approximately -t-250 mV, 600 mV more positive than the ferredoxins. Due to the instability of the protein, a more detailed analysis was not possible until the 1980s, when an analogous protein was isolated from bacterial sources (Fee etal., 1984). The ensuing... 

Tire enzyme does not require lipoic acid. It seems likely that a thiamin-bound enamine is oxidized by an iron-sulfide center in the oxidoreductase to 2-acetyl-thiamin which then reacts with CoA. A free radical intermediate has been detected318 321 and the proposed sequence for oxidation of the enamine intermediate is that in Eq. 15-34 but with the Fe-S center as the electron acceptor. Like pyruvate oxidase, this enzyme transfers the acetyl group from acetylthiamin to coenzyme A. Cleavage of the resulting acetyl-CoA is used to generate ATR An indolepyruvate ferredoxin oxidoreductase has similar properties 322... 

An unusual [2Fe-2S] ferredoxin with unique spectroscopic properties exists in association with cytochromes b and c, and is involved in respiratory electron transport in mitochondria, chloroplasts and certain bacteria. When isolated, the complex contains two b hemes, one c, heme and the 2Fe-2S protein. The 2Fe-2S protein from the bct complex (Sections 62.1.5.2.3 and 62.1.5.2.5) was purified from bovine mitochondria by Rieske et al.,162 and is referred to as the Rieske iron-sulfur protein. The properties of this protein have been reviewed763 and its topography in mitochondrial ubiquinol-cytochrome c reductase has been described.764 They have high redox potentials in the range+150-330 mV. 

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