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Dual nature of the distal histidine residue in the autoxidation reaction of myoglobin and hemoglobin: Comparison of the H64 mutants by Tatsuya Suzuki; Yo‐hei Watanabe; Masashi Nagasawa; Ariki Matsuoka; Keiji Shikama is a Biochemistry, Genetics and Molecular Biology article available to read on EtoBox.

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The oxygenated form of myoglobin or hemoglobin is oxidized easily to the ferric met-form with generation of the superoxide anion. To make clear the possible role(s) of the distal histidine (H64) residue in the reaction, we have carried out detailed pH-dependence studies of the autoxidation rate, using some typical H64 mutants of sperm whale myoglobin, over the wide range of pH 5-12 in 0.1 M buffer at 25 degrees C. Each mutation caused a dramatic increase in the autoxidation rate with the trend H64V >/= H64G >/= H64L >> H64Q > H64 (wild-type) at pH 7.0, whereas each mutant protein showed a characteristic pH-profile which is essentially different from that of the wild-type or native sperm whale MbO2. In particular, all the mutants have lost the acid-catalyzed process that can play a dominant role in the autoxidation reaction of most mammalian myoglobins or hemoglobins. Kinetic analyses of various types of pH-profiles lead us to conclude that the distal histidine residue can play a dual role in the nucleophilic displacement of O2- from MbO2 or HbO2 in protic, aqueous solution. One is in a proton-relay mechanism via its imidazole ring, and the other is in the maximum protection of the

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Author

Tatsuya Suzuki; Yo‐hei Watanabe; Masashi Nagasawa; Ariki Matsuoka; Keiji Shikama

Publisher

John Wiley and Sons; Springer; Wiley (Blackwell Publishing); Springer-Verlag; Blackwell Publishing Inc.; Springer Verlag; Wiley; Springer Science and Business Media LLC (ISSN 1432-1327)

Published

2000

Language

EN

Field

Biochemistry, Genetics and Molecular Biology (Physical Sciences)