Abstract
The ability of myoglobin (Mb) to reversibly bind O 2 and other ligands has been well characterized. Mb also participates with a variety of redox metals to form metmyoglobin ( metMb). By using an anaerobic stopped-flow device we have measured outer-sphere oxidation by [Fe(CN) 6] 3− of native sperm whale myoglobin, recombinant wild-type Mb, and a series of mutant Mb proteins in which the distal His-64 was changed to Gly, Phe, Leu or Val. Second-order rate constants for oxidation of mutant proteins are 10–15 times greater than for recombinant or native ( k ox ~ 10 6 M − s −). We attribute the reduced rate of oxidation of wild-type protein to a higher reorganization energy imposed by the presence of the unique water/His-64/heme interaction, which is absent in the mutant proteins.
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