title: Reactivity and dynamics of H2S, NO, and O2 interacting with hemoglobins from Lucina pectinata.
abstract: Hemoglobin HbI from the clam Lucina pectinata is involved in H2S transport, whereas homologous heme protein HbII/III is involved in O2 metabolism. Despite similar tertiary structures, HbI and HbII/III exhibit very different reactivity toward heme ligands H2S, O2, and NO. To investigate this reactivity at the heme level, we measured the dynamics of ligand interaction by time-resolved absorption spectroscopy in the picosecond to nanosecond time range. We demonstrated that H2S can be photodissociated from both ferric and ferrous HbI. H2S geminately rebinds to ferric and ferrous out-of-plane iron with time constants (τgem) of 12 and 165 ps, respectively, with very different proportions of photodissociated H2S exiting the protein (24% in ferric and 80% in ferrous HbI). The Gln(E7)His mutation considerably changes H2S dynamics in ferric HbI, indicating the role of Gln(E7) in controling H2S reactivity. In ferric HbI, the rate of diffusion of H2S from the solvent into the heme pocket (kentry) is 0.30 μM(-1) s(-1). For the HbII/III-O2 complex, we observed mainly a six-coordinate vibrationally excited heme-O2 complex with O2 still bound to the iron. This explains the low yield of O2 photodissociation and low koff from HbII/III, compared with those of HbI and Mb. Both isoforms behave very differently with regard to NO and O2 dynamics. Whereas the amplitude of geminate rebinding of O2 to HbI (38.5%) is similar to that of myoglobin (34.5%) in spite of different distal heme sites, it appears to be much larger for HbII/III (77%). The distal Tyr(B10) side chain present in HbII/III increases the energy barrier for ligand escape and participates in the stabilization of bound O2 and NO.
authors.affiliation: Department of Chemistry, University of Puerto Rico , Mayagüez Campus, Mayagüez 00680, Puerto Rico.
authors.forename: Cacimar
authors.initials: C
authors.lastname: Ramos-Alvarez
authors.forename: Byung-Kuk
authors.initials: BK
authors.lastname: Yoo
authors.forename: Ruth
authors.initials: R
authors.lastname: Pietri
authors.forename: Isabelle
authors.initials: I
authors.lastname: Lamarre
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Martin
authors.forename: Juan
authors.initials: J
authors.lastname: Lopez-Garriga
authors.forename: Michel
authors.initials: M
authors.lastname: Negrerie
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D049872:Bivalvia; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006860:Hydrogen Bonding; D006862:Hydrogen Sulfide / Q000737:chemistry*; D008024:Ligands; D008969:Molecular Sequence Data; D009569:Nitric Oxide / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D055668:Photochemical Processes; D016415:Sequence Alignment; D013053:Spectrophotometry
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D006454:Hemoglobins; D008024:Ligands; D009569:Nitric Oxide; D010100:Oxygen; D006862:Hydrogen Sulfide