The rubredoxin type centers

Rubredoxin was first described in 1963 by Buchanan [1], and in 1964 by Mortensen [2] during the purification of ferredoxin from Clostridium pasteuriaman. In 1965, Lovenberg and Sobel [3] were able to isolate rubredoxin, a small protein that could replace ferredoxin as an electron carrier in reactions mediated by extracts from C. pasteurianum, and named it rubredoxin (from ruber — red). The chemical feature which, historically, has distinguished rubredoxins from other iron-sulfur proteins. 

In contrast to the large amount of the three-dimensional structural data available in the literature, little is known about the physiological fimction of Rd. Typically, Rds exhibit redox potentials in the range of —60 to OmV [24], and are commonly assmned to be involved in electron transfer processes. It has bear demonstrated that Rd can replace ferredoxin as an electron carrier in certain electron transfer reactions [3]. Furthermore, Rd from the aerobe P. oleovorans was proposed to participate in the ctj-hydroxylation of fatty acids and hydrocarbons by transferring electrons to an alkane hydroxylase [7, 25]. Rd isolated from D. gigas was also shown to be involved in the formation of ATP from the degradation of polyglucose in the presence of 

The visible spectra of Rd and Dx are, in general terms, quite similar, another indication that both proteins contain similar types of iron centers [31]. The typical red color of oxidized Rd and Dx is due to a S — Fe charge-transfer band at 490 and 507 nm, respectively [34]. However, Mossbauer and EPR data for Dx [34, 35] show some differences when compared to Rd, suggesting that the metal ligand geometry and/or coordination environment of these proteins differ. Desulforedoxin and rubredoxin backbones share some similar structural features but show significant differences in terms of metal environment (due to the different cysteine spacing) and water network. 

In the Desulfovibrio species, a large variety of metalloproteins has been isolated and the rubredoxin- and desulforedoxin-like centers can be found in association with other types of mononuclear or dinuclear iron centers as shown in Section 20.5. 

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