The characteristics of the ‘peroxidatic’ reaction of catalase in ethanol oxidation

The results reported show that the experimental results in the study on the ‘microsomal ethanol-oxidation system’ may be reinterpreted and the catalase ‘peroxidatic’ reaction provides a quantitative explanation for the activity hitherto attributed to the ‘microsomal ethanol-oxidation system’

Nozomu Oshino; Reiko Oshino; Britton Chance

2015

Scholarcy highlights

  • Ethanol oxidation by rat liver catalase was studied quantitatively with respect to the rate of H202 generation, catalase haem concentration, ethanol concentration and the steady-state concentration of the catalase-H202 intermediate
  • The results indicate that, whatever the catalase concentration, the magnitude of cyanide inhibition and the range of its effective concentration in the ethanol-oxidation reaction are dependent on the ratio of the H202-generation rate to haem concentration
  • The results described in this paper clearly demonstrate the complexity of the ethanol oxidation by catalase, i.e. under certain conditions, invariance to the catalase concentration, variability of the inhibitor effect and variability of the apparent Km value of ethanol for the ethanol-oxidation reaction
  • These phenomena are explained by changes in the contribution of the 'catalatic' and 'peroxidatic' reactions to the overall decomposition of H202 and can be simplified by introducing, as a parameter, the ratio of the H202generation rate to haem concentration
  • As described in the Results section, this cannot be used as evidence indicating existence of a new 'ethanoloxidation system'. An explanation for these observations is clear in the present study: a small variation in the amount of catalase contaminating the microsomal fraction may make a difference in the ratio of the H202-generation rate to catalase haem concentration, which is one of the key factors in the catalase 'peroxidatic' reaction
  • Since for a given ratio of the H202generation rate to catalase haem concentration, the maximal rate of ethanol oxidation expected corresponds to the rate of H202 generation, the apparent Km values quoted above represent the ethanol concentration causing 50% of H202 to be utilized by the 'peroxidatic' reaction under their conditions
  • As described in the Results section and in the Appendix, a steady-state concentration of the catalase-H202 intermediate reflects a ratio of 'catalatic' and 'peroxidatic' activities

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