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Methionine modification in cytochrome-c peroxidase.

K Kim1, J E Erman

  • 1Department of Chemistry, Northern Illinois University, DeKalb 60115.

Biochimica Et Biophysica Acta
|April 28, 1988
PubMed
Summary

Hydrogen peroxide modifies specific methionine residues in apocytochrome-c peroxidase. Modification of Met-230/Met-231 pair is crucial for forming Compound I, essential for enzyme activity.

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Area of Science:

  • Biochemistry
  • Enzymology
  • Protein chemistry

Background:

  • Cytochrome-c peroxidase is a key enzyme in cellular defense mechanisms.
  • Methionine residues in proteins can be susceptible to oxidation by reactive oxygen species.
  • Understanding the role of specific methionine residues is vital for enzyme function.

Purpose of the Study:

  • To investigate the oxidation of methionine residues in apocytochrome-c peroxidase by hydrogen peroxide.
  • To determine the functional consequences of methionine oxidation on heme binding and enzymatic activity.
  • To identify critical methionine residues involved in the formation of Compound I.

Main Methods:

  • Oxidation of apocytochrome-c peroxidase with hydrogen peroxide under controlled pH and buffer conditions.
  • Spectroscopic analysis (UV-Vis) to characterize heme binding and spectral shifts.
  • Enzyme kinetics to assess cyanide binding affinity and Compound I formation.

Main Results:

  • Hydrogen peroxide selectively oxidized Met-119, Met-230, and Met-231 to sulfoxides at equal rates.
  • Apoenzyme with up to two oxidized methionine residues bound heme stoichiometrically.
  • Heme-reconstituted modified enzyme showed a red-shifted Soret maximum, indicating heme environment perturbation.
  • Modified enzyme retained cyanide binding affinity but lost the ability to form Compound I, correlated with Met-230/Met-231 modification.

Conclusions:

  • Methionine residues Met-119, Met-230, and Met-231 are susceptible to oxidation by hydrogen peroxide.
  • Modification of the Met-230/Met-231 pair is essential for the formation of Compound I in cytochrome-c peroxidase.
  • Oxidation of these residues perturbs the heme environment and impairs the enzyme's catalytic function.

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