Reactivity and Dynamics of H2S, NO, and O2 Interacting with Hemoglobins from Lucina pectinata

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• 作者：Cacimar Ramos-Alvarez ; Byung-Kuk Yoo ; Ruth Pietri ; Isabelle Lamarre ; Jean-Louis Martin ; Juan Lopez-Garriga ; Michel Negrerie
• 刊名：Biochemistry
• 出版年：2013
• 出版时间：October 8, 2013
• 年：2013
• 卷：52
• 期：40
• 页码：7007-7021
• 全文大小：893K
• 年卷期：v.52,no.40(October 8, 2013)
• ISSN：1520-4995

文摘

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 (蟿_gem) 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 (k_entry) is 0.30 渭M^鈥? s^鈥?. For the HbII/III鈥揙₂ complex, we observed mainly a six-coordinate vibrationally excited heme鈥揙₂ complex with O₂ still bound to the iron. This explains the low yield of O₂ photodissociation and low k_off 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.