5 K extended x-ray absorption fine structure and 40 K 10-s resolved extended x-ray absorption fine structure studies of photolyzed carboxymyoglobin

• Published in: Biochemistry (Easton) Vol. 26; no. 25; pp. 8066 - 8072
• Main Authors: Teng, Tsu Yi, Huang, Huey W, Olah, Glenn A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.12.1987
• Subjects: Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Heme; Interactions. Associations; Intermolecular phenomena; Molecular biophysics; Myoglobin - metabolism; Photolysis; Protein Conformation; Spectrum Analysis - instrumentation; Spectrum Analysis - methods; X-Rays; Reaction intermediate; Myoglobin; Hemoprotein; Laser beam; Very low temperature; Photodissociation; Molecular dissociation; EXAFS spectrometry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00399a007

A previous extended X-ray absorption fine structure (EXAFS) study of photolyzed carboxymyoglobin (MbCO) [Chance, B., Fischetti, R., & Powers, L. (1983) Biochemistry 22, 3820-3829; Powers, L., Sessler, J. L., Woolery, G. L., & Chance, B. (1984) Biochemistry 23, 5519-5523] has provoked much discussion on the heme structure of the photoproduct (MbCO). The EXAFS interpretation that the Fe-CO distance increases by no more than 0.05 A following photodissociation has been regarded as inconsistent with optical, infrared, and magnetic susceptibility studies [Fiamingo, F. G., & Alben, J. O. (1985) Biochemistry 24, 7964-7970; Sassaroli, M., & Rousseau, D. L. (1986) J. Biol. Chem. 261, 16292-16294]. The present experiment was performed with well-characterized dry film samples in which MbCO molecules were embedded in a poly(vinyl alcohol) matrix [Teng, T. Y., & Huang, H. W. (1986) Biochim. Biophys. Acta 874, 13-18]. The sample had a high protein concentration (12 mM) to yield adequate EXAFS signals but was very thin (40 micron) so that complete photolysis could be easily achieved by a single flash from a xenon lamp. Although the electronic state of MbCO resembles that of deoxymyoglobin (deoxy-Mb), direct comparison of EXAFS spectra indicates that structurally MbCO is much closer to MbCO than to deoxy-Mb.