Carbon dioxide mediates Mn(II)-catalyzed decomposition of hydrogen peroxide and peroxidation reactions

Abstract

Mn(II) can catalyze the decomposition of H2O2 and, in the presence of H 2O2, can catalyze the oxidation of NADH. Strikingly, these processes depend on the simultaneous presence of both CO 2 and HCO 3 ؊ . This explains the exponential dependence of the rates on Materials and MethodsNaHCO 3 , MnCl 2 , sodium pyrophosphate, and H 2 O 2 were from Mallinckrodt; Tris was from Merck; catalase was from Roche Molecular Biochemicals; human MnSOD was from Biotechnology General (Rehovot, Israel); and NADH was from Sigma. Reaction mixtures usually contained 10 mM H 2 O 2 , 0.1 mM MnCl 2 , and 20 mM NaHCO 3 in 100 mM Tris buffer at pH 7.4 and room temperature (23°C). Reactions were followed spectrophotometrically, and in cases where the addition of reactants entailed sudden changes in absorbance, due either to dilution or the absorbance of the reagent added, such changes were corrected in the data shown. When absorbance changes with time were too rapid to record, they are shown as dashed lines as in Fig. 3. CO 2 was added as ice-cold water saturated with CO 2 gas. ResultsAbsorption Spectra. Addition of the third component (H 2 O 2 or MnCl 2 , or NaHCO 3 ), to Tris-buffered solutions of the other two, initiated the changes in absorption spectrum shown in Fig. 1. It should be noted that several buffering species were explored, including phosphate, cacodylate, and Hepes, but only Tris supported the changes observed. Fig. 1 A shows that the most rapid (0 -3 min) was an increase in absorbance in the range of 250 -350 nm and a decrease at wavelengths Ͻ250 nm. At longer reaction times (0 -20 min), absorbance appeared at Ϸ270 nm, whereas the absorbance Ͻ250 nm first decreased and then increased, as shown in Fig. 1B. At still longer times (Fig. 1C), the band at Ϸ270 nm became more pronounced, a shoulder developed at Ϸ300 nm, and absorbance Ͻ250 nm decreased.The species responsible for the absorbance centered at 270 nm is some stable product of Tris oxidation, as similar absorbance is seen in Tris buffer that has aged for many months. The kinetics of the absorbance change at 270 nm is shown in Fig. 2. Starting the reaction by adding NaHCO 3 caused a small but rapid increase at 270 nm, which was followed by a slower increase that was not interrupted by late addition of 48 g͞ml MnSOD, 0.5 mM pyrophosphate, or 120 units͞ml catalase, any of which inhibited if present at the outset. The initial rapid increase at 270 nm was due to the rapidly formed species absorbing in the 250-to 350-nm region. Evidently, the stable A 270 species is produced from a preformed precursor and does not depend on the continued presence of H 2 O 2 , O 2 Ϫ , or Mn(III). The latter deduction is based on the abilities of catalase to remove H 2 O 2 , MnSOD to remove O 2 Ϫ , and pyrophosphate to complex and thus trap Mn(III).The time course of the broad band followed at Ϸ300 nm is illustrated in Fig. 3. Addition of NaHCO 3 to the buffered solution of Mn(II) ϩ H 2 O 2 caused a rapid increase in absorbance that approached a plateau. This plateau evidently represented a...

Reactive oxygen species‐dependent destruction of MEK and Akt in Manumycin stimulated death of lymphoid tumor and myeloma cell lines

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Copper-catalyzed Protein Oxidation and Its Modulation by Carbon Dioxide

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