The role of CO2 in cobalt-catalyzed peroxidations.
Augmentation, by CO(2)/HCO(3)(-), of Co(II)-catalyzed peroxidations was explored to clarify whether the rate enhancement was due to CO(2) or to HCO(3)(-). The rate of oxidation of NADH by Co(II) plus H(2)O(2), in Tris or phosphate, was markedly enhanced by CO(2)/HCO(3)(-). Phosphate was seen to inhibit the Co(II)-catalyzed peroxidation, probably due to its sequestration of the Co(II). When CO(2) was used, there was an initial burst of NADH oxidation followed by a slower linear rate. The presence of carbonic anhydrase eliminated this initial burst; establishing that CO(2) rather than HCO(3)(-) was the species responsible for the observed rate enhancements. Both kinetic and spectral data indicated that Co(II) was converted by H(2)O(2) into a less active form from which Co(II) could be regenerated. This less active form absorbed in both the UV and visible regions, and is assumed to be a peroxy bridged binuclear complex. The rate of formation of this absorbing form was increased by HCO(3)(-)/CO(2). A minimal mechanism consistent with these observations is proposed.
Liochev
Stefan I
SI
The Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
Fridovich
Irwin
I
D002245:Carbon Dioxide / Q000737:chemistry*; D002256:Carbonic Anhydrases / Q000737:chemistry*; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry*; D009243:NAD / Q000737:chemistry; D010084:Oxidation-Reduction; D010710:Phosphates / Q000737:chemistry
D010710:Phosphates; D009243:NAD; D002245:Carbon Dioxide; D003035:Cobalt; D006861:Hydrogen Peroxide; D002256:Carbonic Anhydrases