Rubredoxin

Rubredoxins are a class of low-molecular-weight iron-containing proteins found in sulfur-metabolizing bacteria and archaea. Sometimes rubredoxins are classified as iron-sulfur proteins; however, in contrast to iron-sulfur proteins, rubredoxins do not contain inorganic sulfide. Like cytochromes, ferredoxins and Rieske proteins, rubredoxins participate in electron transfer in biological systems.

Structure
The 3-D structures of a number of rubredoxins have been solved. The fold belongs to the α+β class, with 2 α-helices and 2-3 β-strands. Rubredoxin active site contains an iron ion which is coordinated by the sulfurs of four conserved cysteine residues forming an almost regular tetrahedron. This is sometimes denoted as a [1Fe-0S] or an Fe1S0 system, in analogy to the nomenclature for iron-sulfur proteins.

Rubredoxins perform one-electron transfer processes. The central iron atom changes between the +2 and +3 oxidation states. In both oxidation states, the metal remains high spin, which helps to minimize structural changes. The reduction potential of a rubredoxin is typically in the range +50 mV to -50 mV.



Rubredoxin in some biochemical reactions
camphor 1,2-monooxygenase [(+)-camphor,reduced-rubredoxin:oxygen oxidoreductase (1,2-lactonizing)]
 * (+)-bornane-2,5-dione + reduced rubredoxin + O2 = 5-oxo-1,2-campholide + oxidized rubredoxin + H2O

alkane 1-monooxygenase (alkane,reduced-rubredoxin:oxygen 1-oxidoreductase)
 * octane + reduced rubredoxin + O2 = 1-octanol + oxidized rubredoxin + H2O

superoxide reductase (rubredoxin:superoxide oxidoreductase)
 * reduced rubredoxin + superoxide + 2 H+ = rubredoxin + H2O2

rubredoxin&mdash;NAD+ reductase (rubredoxin:NAD+ oxidoreductase)
 * reduced rubredoxin + NAD+ = oxidized rubredoxin + NADH + H+

rubredoxin&mdash;NAD(P)+ reductase (rubredoxin:NAD(P)+ oxidoreductase)
 * reduced rubredoxin + NAD(P)+ = oxidized rubredoxin + NAD(P)H + H+