title: CO, NO and O2as Vibrational Probes of Heme Protein Interactions.
abstract: The gaseous XO molecules (X = C, N or O) bind to the heme prosthetic group of heme proteins, and thereby activate or inhibit key biological processes. These events depend on interactions of the surrounding protein with the FeXO adduct, interactions that can be monitored via the frequencies of the Fe-X and X-O bond stretching modes, νFeX and νXO. The frequencies can be determined by vibrational spectroscopy, especially resonance Raman spectroscopy. Backbonding, the donation of Fe dπelectrons to the XO π* orbitals, is a major bonding feature in all the FeXO adducts. Variations in backbonding produce negative νFeX/νXO correlations, which can be used to gauge electrostatic and H-bonding effects in the protein binding pocket. Backbonding correlations have been established for all the FeXO adducts, using porphyrins with electron donating and withdrawing substituents. However the adducts differ in their response to variations in the nature of the axial ligand, and to specific distal interactions. These variations provide differing vantages for evaluating the nature of protein-heme interactions. We review experimental studies that explore these variations, and DFT computational studies that illuminate the underlying physical mechanisms.
authors.affiliation: Department of Chemistry, University of Washington Box 351700, Seattle, Washington 98195.
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Spiro
authors.forename: Alexandra V
authors.initials: AV
authors.lastname: Soldatova
authors.forename: Gurusamy
authors.initials: G
authors.lastname: Balakrishnan
keywords: Backbonding; Carbon monoxide; DFT; Dioxygen; Heme; Infrared; Nitric oxide; Protein; Raman