Oxidation of deoxy myoglobin by [Fe(CN)(6)](3-)

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 meta ls 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 protei ns in which the distal His-64 was changed to Gly, Phe, Leu or Val. Second-o rder rate constants for oxidation of mutant proteins are 10-15 times greate r than for recombinant or native (k(ox)similar to 10(6)M(-1)s(-1)). We attr ibute the reduced rate of oxidation of wild-type protein to a higher reorga nization energy imposed by the presence of the unique water/His-64/heme int eraction, which is absent in the mutant proteins. (C) 1999 Elsevier Science Inc. All rights reserved.