Kinetic modulation in carbonmonoxy derivatives of truncated hemoglobins: The role of distal heme pocket residues and extended apolar tunnel

Uri Samuni, David Dantsker, Anandhi Ray, Jonathan B. Wittenberg, Beatrice A. Wittenberg, Sylvia Dewilde, Luc Moens, Yannick Ouellet, Michel Guertin, Joel M. Friedman

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Abstract

Truncated hemoglobins (trHbs), are a distinct and newly characterized class of small myoglobin-like proteins that are widely distributed in bacteria, unicellular eukaryotes, and higher plants. Notable and distinctive features associated with trHbs include a hydrogen-bonding network within the distal heme pocket and a long apolar tunnel linking the external solvent to the distal heme pocket. The present work compares the geminate and solvent phase rebinding kinetics from two trHbs, one from the ciliated protozoan Paramecium caudatum (P-trHb) and the other from the green alga Chlamydomonas eugametos (C-trHb). Unusual kinetic patterns are observed including indications of ultrafast (picosecond) geminate rebinding of CO to C-trHb, very fast solvent phase rebinding of CO for both trHbs, time-dependent biphasic CO rebinding kinetics for P-trHb at low CO partial pressures, and for P-trHb, an increase in the geminate yield from a few percent to nearly 100% under high viscosity conditions. Species-specific differences in both the 8-ns photodissociation quantum yield and the rebinding kinetics, point to a pivotal functional role for the E11 residue. The response of the rebinding kinetics to temperature, ligand concentration, and viscosity (glycerol, trehalose) and the viscosity-dependent changes in the resonance Raman spectrum of the liganded photoproduct, together implicate both the apolar tunnel and the static and dynamic properties of the hydrogen-bonding network within the distal heme pocket in generating the unusual kinetic patterns observed for these trHbs.

Original languageEnglish (US)
Pages (from-to)27241-27250
Number of pages10
JournalJournal of Biological Chemistry
Volume278
Issue number29
DOIs
Publication statusPublished - Jul 18 2003

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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