Analysis of the high- and low-spin soret bands of horse-heart metmyoglobin complexes

Interest in the thermodynamics of the iron‐binding site in hemoproteins has increased in recent years due to refinements in x‐ray crystallographic studies of hemoproteins [see Deathage, J. F., Lee, R. S., Anderson, C. M. & Moffat, K. (1976) J. Mol. Biol. 104, 687–706; Heidner, E. J., Ladner, R. C. & Perutz, M. F. (1976) J. Mol. Biol. 104, 707–722; Deathage, J. F., Lee, R. S. & Moffat, K. (1976) J. Mol. Biol. 104, 723–728; Ladner, R. C., Heidner, E. J. & Perutz, M. F. (1976) J. Mol. Biol. 114, 385–414; Fermi, G. & Perutz, M. F. (1977) J. Mol. Biol. 114, 421–431; Takano, T. (1977) J. Mol. Biol. 110, 537–568 and 569–589], the synthesis and x‐ray analysis of model heme compounds [see Scheidt, W. R. (1977) Acc. Chem. Res. 10, 339–345; Kastner, M. E., Scheidt, W. R., Mashino, T. & Reed, C. A. (1978) J. Am. Chem. Soc. 100, 666–667; Mashiko, T., Kastner, M. E., Spartalian, K., Scheidt, W. R. & Reed, C. A. (1978) J. Am. Chem. Soc. 100, 6354–6362; Hill, H. A. O., Skite, P. P., Buchler, J. W., Luchr, H., Tonn, M., Gregson, A. K. & Pellizer, G. (1979) Chem. Commun. 4, 151–152; and Scheidt, W. R., Cohen, I. A. & Kastner, M. E. (1979) Biochemistry 18, 3546–3556], and the numerous data on heme–protein interactions that account for the differences observed in ligand binding between the various species of animals. Numerous probes have been used and provide information about the structure and thermodynamics of the binding site, but no single probe can provide the complete picture [see Iizuka, T. & Yonetani, T. (1970) Adv. Biophys. 1, 157–182; Smith, D. W. & Williams, R. J. P. (1970) Struct. Bond. 7, 1–45; and Spiro, T. G. (1975) Biochim. Biophys. Acta 416, 169–189].