Cobalt -rubredoxin

Okamura T-A, Takamizawa S, Ueyama N, Nakamura A (1998) Novel rubredoxin model tetrathiolato iron(II) and cobalt(II) complexes containing intramolecular single and double NH S hydrogen bonds. Inorg Chem 37 18-28... 

Chemical studies of rubredoxins have led to the replacement of the Fe with an Fc4S4 center, with Co, and with Ni. The Co replacement of Fe , in P. oleovorans rubredoxin, leads to a stable protein that displays reduced (but not trivial) reactivity in the w-hydroxylation reaction. The spectral properties of the cobalt(II) site show the expected changes in d-d bands and the expected shifts in charge-transfer transitions. Interestingly, when Ni " is substituted into rubredoxins from desulfovibrio species, the resultant proteins show hydrogenase activity. ... 

The rate of reduction of cytochrome c by the cobalt-substituted analogue of rubredoxin is a factor of 2.25 lower than the rate with rubredoxin itself. Both proteins mediate the reduction of cytochrome c in the presence of NADH and the decrease in the rate is attributed to the decreased efficiency in oxidation of cobalt(ii) compared with iron(ii). Reduction of cytochrome c by NADPH is catalysed by an adrenodoxin reductase-adrenodoxin complex in which the rate-determining step is electron transfer from the flavin (FAD) of the reductase to the FeaS2 centre of adrenodoxin. The pH dependence of the rate shows a pATa of 6.75, with the high-pH form 27.5 times more reactive than the low-pH form. Both NADPH reduction of the complex and cytochrome c oxidation of the complex were faster than the catalytic rate. Catalytic roles of four iron-sulphur centres in trimethylene dihydrogenase and ferredoxin nitrite reductase have also been examined. Synthetic analogues of four iron ferredoxins have also attracted much attention. - ... 

---