title: Insights into the anomalous heme pocket of rainbow trout myoglobin.
abstract: Rainbow trout myoglobin (Mb) is characterized by an unusually low affinity for oxygen, having a P(50) of 4.92±0.29 mm Hg at 25 °C which is the highest ever reported for any vertebrate Mb at the same temperature (Helbo and Fago, (2011) Am. J. Physiol. Regul. Integr. Comp. Physiol. 300, R101-R108). In order to gain insight into the structural factors of the heme pocket that may be important determinants for this atypical oxygen affinity, we have carried out an electronic absorption and resonance Raman characterization of the ferric and ferrous protein with and without exogenous ligands (O(2), CO, F(-)) and compared the results with those of other Mbs. While the ν(Fe-His) stretch appears at a frequency similar to other vertebrate Mbs, the resonance Raman frequencies of the Fe-ligand stretching modes reveal significant variations in the interaction of iron-bound ligands with distal residues. In particular, the spectroscopic characterization highlights two exceptional properties of rainbow trout Mb, a significantly higher level of reversed heme and reduced hydrogen bonding interactions between ligands and the distal HisE7 residue compared with other Mbs. The weakening of the hydrogen bond interaction is proposed to be the primary cause of the significantly reduced oxygen affinity.
authors.affiliation: Dipartimento di Chimica Ugo Schiff, Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino, Italy.
authors.forename: Barry D
authors.initials: BD
authors.lastname: Howes
authors.forename: Signe
authors.initials: S
authors.lastname: Helbo
authors.forename: Angela
authors.initials: A
authors.lastname: Fago
authors.forename: Giulietta
authors.initials: G
authors.lastname: Smulevich
mesh_terms: D000818:Animals; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism; D005459:Fluorides / Q000737:chemistry / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D009211:Myoglobin / Q000737:chemistry* / Q000378:metabolism; D017686:Oncorhynchus mykiss / Q000097:blood*; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman
chemical_list: D009211:Myoglobin; D006418:Heme; D002248:Carbon Monoxide; D005459:Fluorides; D010100:Oxygen