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Oxymyohemerythrin: discriminating between O2 release and autoxidation
C R Lloyd1, G M Raner, A Moser
1Department of Chemistry, University of Utah, Salt Lake City 84112, USA.
Journal of Inorganic Biochemistry
|November 7, 2000
Summary
Myohemerythrin (Mhr), an oxygen carrier, undergoes distinct reactions including O2 release and autoxidation. Environmental factors significantly influence these processes, with specific mutations like L103V/N dramatically accelerating autoxidation.
Area of Science:
- Biochemistry
- Protein Chemistry
- Biophysical Chemistry
Background:
- Myohemerythrin (Mhr) is a non-heme iron O2 carrier found in marine worms.
- OxyMhr can release O2 or undergo autoxidation, producing hydrogen peroxide and metMhr.
- Anions can promote Mhr autoxidation.
Purpose of the Study:
- To investigate environmental effects on Mhr's O2 release and autoxidation reactions.
- To compare kinetic parameters of O2 release versus autoxidation.
- To explore the role of specific mutations and anions in Mhr reactivity.
Main Methods:
- Utilized recombinant Themiste zostericola Mhrs.
- Measured kinetic parameters (deltaV‡, deltaH‡, deltaS‡) for O2 release and autoxidation.
- Investigated reactions with and without sodium azide, and studied L103V/N mutants.
Main Results:
- O2 release and autoxidation exhibit distinct thermodynamic and kinetic parameters.
- Autoxidation is significantly accelerated by sodium azide.
- L103V and L103N oxyMhr mutants autoxidize 10^3-10^5 times faster than wild-type Mhr.
Conclusions:
- Leucine-103 is crucial for stabilizing bound dioxygen, potentially acting as a protein gate.
- The rate-limiting steps for Mhr autoxidation and anation are not solely ligand binding.
- Environmental factors and protein structure play key roles in Mhr's oxygen-binding and reaction dynamics.