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On the formation and reactivity of compound I of the His-64 myoglobin mutants
T Matsui1, S i Ozaki, Y Watanabe
1Department of Structural Molecular Science, The Graduate University for Advanced Studies, Myodaiji, Okazaki 444, Japan.
Abstract:
Myoglobin (Mb) catalyzes various two-electron oxidations; however, ferryl porphyrin cation radical equivalent to peroxidase compound I has not been identified yet. Distal histidine mutants of sperm whale Mb (His-64 --> Ala, Ser, and Leu) afford an apparent intermediate followed by the formation of a ferryl heme (Mb-II) in the reaction with m-chloroperbenzoic acid. Because the intermediate exhibits characteristic absorption spectrum of compound I and bears two electron oxidizing equivalents above the ferric state, we have assigned the species as compound I of myoglobin (Mb-I). Although we have recently observed compound I of the F43H/H64L Mb mutant, F43H and wild type Mb react with m-chloroperbenzoic acid to give Mb-II without any accumulation of Mb-I. The results unambiguously indicate that His-64 plays a key role in destabilizing wild type Mb-I. Furthermore, Mb-I is found to be capable of performing two-electron oxidation of styrene, thioanisole, and H2O2.
Insights
Researchers identified myoglobin compound I (Mb-I) in distal histidine mutants, revealing His-64
Area of Science:
- Biochemistry
- Enzymology
- Protein Chemistry
Background:
- Myoglobin (Mb) is known to catalyze two-electron oxidations.
- The identification of ferryl porphyrin cation radical, equivalent to peroxidase compound I, in myoglobin has been elusive.
Purpose of the Study:
- To identify and characterize compound I of myoglobin (Mb-I).
- To investigate the role of distal histidine (His-64) in the stability and reactivity of Mb-I.
Main Methods:
- Spectroscopic analysis of distal histidine mutants of sperm whale myoglobin (His-64 --> Ala, Ser, Leu) reacted with m-chloroperbenzoic acid.
- Characterization of reaction intermediates and final products.
Main Results:
- An intermediate with the characteristic absorption spectrum of compound I was observed in distal histidine mutants.
- This intermediate, assigned as myoglobin compound I (Mb-I), possesses two electron oxidizing equivalents above the ferric state.
- Wild type and F43H Mb react to form ferryl heme (Mb-II) without accumulating Mb-I, indicating His-64 destabilizes Mb-I.
Conclusions:
- Distal histidine mutants of myoglobin can form and stabilize compound I.
- His-64 plays a crucial role in destabilizing wild type myoglobin compound I.
- Myoglobin compound I is capable of catalyzing two-electron oxidations of various substrates, including styrene, thioanisole, and H2O2.