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Related Experiment Videos

Ligand migration in sperm whale myoglobin

E E Scott1, Q H Gibson

  • 1Department of Biochemistry and Cell Biology, Rice University, 6100 Main Street, Houston, Texas 77005, USA. yertle@bioc.rice.edu

Biochemistry
|October 8, 1997
PubMed
Summary

Investigating oxymyoglobin mutants reveals two oxygen rebinding phases, influenced by xenon. Xenon alters these geminate reactions, providing insights into ligand movement within myoglobin.

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Area of Science:

  • Biochemistry
  • Biophysics
  • Protein Dynamics

Background:

  • Myoglobin stores and transports oxygen.
  • Understanding oxygen dynamics in myoglobin is crucial for its function.
  • Geminate rebinding describes the initial steps of ligand-protein interaction after photodissociation.

Purpose of the Study:

  • To investigate the nanosecond to microsecond geminate oxygen rebinding kinetics in over 25 oxymyoglobin point mutants.
  • To determine the effects of xenon binding on these geminate rebinding processes.
  • To elucidate the role of specific protein interior locations and xenon binding sites in ligand recombination.

Main Methods:

  • Time-resolved spectroscopy following photolysis of oxymyoglobin.
  • Studying over 25 oxymyoglobin point mutants.
  • Conducting experiments in the presence and absence of 12 atm xenon.
  • Utilizing known xenon binding sites and molecular dynamics simulations.

Main Results:

  • Two distinct geminate oxygen rebinding phases were observed: a fast phase (20 ns halftime) and a slower phase (0.5-2 µs halftime).
  • Xenon generally accelerated the fast phase but slowed and diminished the amplitude of the slower phase.
  • The rates and proportions of these phases, and xenon's effects, varied significantly among different mutants.
  • Evidence suggests photodissociated ligands occupy xenon sites 4 (distal pocket) and 1 (below heme) for slower rebinding.

Conclusions:

  • Geminate oxygen rebinding in myoglobin involves at least two distinct pathways on the nanosecond to microsecond timescale.
  • Xenon binding influences these pathways by interacting with specific protein sites, affecting ligand recombination dynamics.
  • The observed variations highlight the intricate relationship between protein structure, ligand proximity, and recombination kinetics in myoglobin.

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