Monooxygenase activity of type 3 copper proteins
Shinobu Itoh1, Shunichi Fukuzumi
1Department of Chemistry, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan. shinobu@sci.osaka-cu.ac.jp
Accounts of Chemical Research
|April 28, 2007
Summary
Type 3 copper proteins
Area of Science:
- Biochemistry
- Bioinorganic Chemistry
- Enzymology
Background:
- Type 3 copper proteins, including tyrosinase and hemocyanin, play crucial roles in biological oxidation reactions.
- Understanding their monooxygenase (phenolase) activity is key to elucidating complex biochemical pathways.
- Model systems are essential for dissecting the intricate reaction mechanisms of these metalloenzymes.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying the monooxygenase (phenolase) activity of type 3 copper proteins.
- To differentiate between reaction pathways involving neutral phenols and phenolates.
- To investigate the enzymatic mechanisms of tyrosinase and hemocyanin using model compound insights.
Main Methods:
- Utilized side-on peroxo dicopper(II) model compounds and bis(mu-oxo)dicopper(III) complexes.
- Employed Marcus theory of electron transfer and Hammett analysis for mechanistic interpretation.
- Investigated enzymatic reactions of tyrosinase and hemocyanin, including the use of urea as an additive.
Main Results:
- Neutral phenols react via a proton-coupled electron-transfer (PCET) mechanism involving phenoxyl radicals.
- Lithium phenolates react via an electrophilic aromatic substitution mechanism yielding catechols.
- Enzymatic reactions of tyrosinase and hemocyanin demonstrate similar electrophilic aromatic substitution and ionic mechanisms, respectively.
Conclusions:
- The reaction mechanism of type 3 copper proteins' monooxygenase activity is highly dependent on the substrate's protonation state.
- Model systems effectively mimic and help elucidate the complex enzymatic mechanisms of tyrosinase and hemocyanin.
- This study provides a unified mechanistic understanding of phenol oxidation by type 3 copper proteins.
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