title: Conformational substates and dynamic properties of carbonmonoxy hemoglobin.
abstract: Heme pocket dynamics of human carbonmonoxy hemoglobin (HbCO) is studied by Fourier transform infrared spectroscopy. The CO stretching band at various temperatures in the interval 300-10 K is analyzed in terms of three taxonomic A substates; however, in HbCO the band attributed to the A(1) taxonomic substate accounts for approximately 90% of the total intensity in the pH range 8.8-4.5. Two different regimes as a function of temperature are observed: below 160 K, the peak frequency and the bandwidth of the A(1) band have constant values whereas, above this temperature, a linear temperature dependence is observed, suggesting the occurrence of transitions between statistical substates within the A(1) taxonomic substate in this protein. The relationship between the heme pocket dynamics (as monitored by the thermal behavior of the CO stretching band), the overall dynamic properties of the protein matrix (as monitored by the thermal behavior of Amide II and Amide I' bands) and the glass transition of the solvent (as monitored by the thermal behavior of the bending band of water) is also investigated. From this analysis, we derive the picture of a very soft heme pocket of hemoglobin characterized by rather large anharmonic terms and strongly coupled to the dynamic properties of the solvent.
authors.affiliation: Istituto Nazionale per la Fisica della Materia and Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, Via Archirafi, 36, 90123 Palermo, Italy. cupane@fisicia.unipa.it
authors.forename: Antonio
authors.initials: A
authors.lastname: Cupane
authors.forename: Maurizio
authors.initials: M
authors.lastname: Leone
authors.forename: Valeria
authors.initials: V
authors.lastname: Militello
mesh_terms: D000577:Amides / Q000737:chemistry; D002263:Carboxyhemoglobin / Q000737:chemistry*; D006418:Heme / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D011487:Protein Conformation; D012997:Solvents / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature
chemical_list: D000577:Amides; D008024:Ligands; D012997:Solvents; D006418:Heme; D002263:Carboxyhemoglobin