Assignment of the Heme Axial Ligand(s) for the Ferric Myoglobin (H93G) and Heme Oxygenase (H25A) Cavity Mutants as Oxygen Donors Using Magnetic Circular Dichroism†

• Main Authors: Alycen E. Pond, Mark P. Roach, Masanori Sono, Ann Huff Rux, Stefan Franzen, Robert Hu, Melissa R. Thomas, Angela Wilks, Yi Dou, Masao Ikeda-saito, Paul R. Ortiz De Montellano, William H. Woodruff, Steven G. Boxer, John H. Dawson
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1998
• Subjects: Sperm whale
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.548.875; http://www.stanford.edu/group/boxer/papers/paper172.pdf

ABSTRACT: UV-visible absorption and magnetic circular dichroism (MCD) data are reported for the cavity mutants of sperm whale H93G myoglobin and human H25A heme oxygenase in their ferric states at 4 °C. Detailed spectral analyses of H93G myoglobin reveal that its heme coordination structure has a single water ligand at pH 5.0, a single hydroxide ligand at pH 10.0, and a mixture of species at pH 7.0 including five-coordinate hydroxide-bound, and six-coordinate structures. The five-coordinate aquo structure at pH 5 is supported by spectral similarity to acidic horseradish peroxidase (pH 3.1), whose MCD data are reported herein for the first time, and acidic myoglobin (pH 3.4), whose structures have been previously assigned by resonance Raman spectroscopy. The five-coordinate hydroxide structure at pH 10.0 is supported by MCD and resonance Raman data obtained here and by comparison with those of other known five-coordinate oxygen donor complexes. In particular, the MCD spectrum of alkaline ferric H93G myoglobin is strikingly similar to that of ferric tyrosinate-ligated human H93Y myoglobin, whose MCD data are reported herein for the first time, and that of the methoxide adduct of ferric protoporphyrin IX dimethyl