Carbon monoxide oxidoreductase

Electron-nuclear double-resonance studies aconitase, 38 326-328 [4Fe0134S] cluster, 38 355-358 Electron paramagnetic resonance carbon monoxide oxidoreductase, 32 326-328... 

Both hydrogenases and carbon monoxide oxidoreductases contain iron-sulfur clusters in addition to nickel. It may be noted that in addition to the Ni hydrogenases, there is another class of Fe hydrogenases, such as those in clostridia, which contain no nickel but have a specialized type of iron-sulfur cluster (28a, 28b). Therefore, it has to be established that the nickel in Ni hydrogenases is the active site as will be seen later, there is a considerable amount of circumstantial evidence for this. 

Carbon monoxide oxidoreductase (carbon monoxide dehydrogenase) catalyzes the interconversion of CO and COz with suitable electron acceptors and donors. The reaction takes place via an enzyme-bound one-carbon intermediate ... 

The reaction [Eq. (7)] requires a disulfide-reducing system such as dithiothreitol or disulfide reductase and a reducing agent such as NADPH or reduced ferredoxin. It is proposed [Eq. (5)] that carbon monoxide oxidoreductase binds CO as a one-carbon intermediate [C,], which can be either oxidized to C02 or condensed with the methyl group of a methylated corrinoid protein and CoA in the final step of acetyl-CoA synthesis. 

Carbon monoxide oxidoreductase has a high molecular weight values between 150,000 and 460,000 have been reported (25). Analysis of the enzyme from C. thermoaceticum indicated a composition of 2 atoms of Ni, 1 Zn, 11 Fe, and 14 inorganic sulfide per dimeric enzyme, with a relative molecular mass of approximately 150,000 Da (23). 

Fig. 14. EPR spectra of carbon monoxide oxidoreductase from C. thermoaceticum, treated with CO plus coenzyme A. Solid lines are experimental spectra, dashed lines are computer simulations, with gx= gf = 2.074, g2 = 2.028. Substitutions with 61Ni and 57Fe were made by growth of the organism on the appropriate isotopes, (a) Effect of substitution with 6lNi. Simulation assumes AM = 3 MHz, A, = 20 MHz. (b, p. 328) Effects of substitution with 5,Fe and l3C. The simulation of the 57Fe spectrum assumes one iron atom with Ah = 40 MHz, A = 60 MHz, and two iron atoms with A, = 20 MHz, A = 30 MHz. The simulation of the l3C spectrum assumes An = 26 MHz, A = 13 MHz. Spectra provided by courtesy of Dr. S. G, Ragsdale.

Carbon monoxide oxidoreductase Bacterial CC2P2Y2 (MPTpC)Mo( ) Unknown 4 Fe2S2, 2 FAD, Se 43,266... 

Carbon monoxide oxidoreductase has been employed by Turner et al. (1984) in an attempt to construct a novel CO sensor. The enzyme, which was isolated from Pseudomonas thermocarboxydovorans, has a molecular weight of 270 000 and contains FAD, FeS, and molybdenum as redox active groups. It catalyzes the oxidation of CO to CO2 using various electron acceptors, e.g. NMP+ or oxygen. The temperature optimum of the raction is 80°C. The KM value for CO is as low as 0.5 pmol/1 acetylene and cyanide inhibit the enzymatic reaction. 

Figure 7. The cyclic voltammogram of a solution containing cytochrome c and caibon monoxide (a) as in (a) but with the enzyme, carbon monoxide oxidoreductase added.

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