Oxymyohemerythrin: discriminating between O2 release and autoxidation

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Gregory M. Raner, Associate Professor and Graduate Director (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site: http://library.uncg.edu/

Abstract: Myohemerythrin (Mhr) is a non-heme iron O2 carrier (with two irons in the active site) that is typically found in the retractor muscle of marine ‘peanut’ worms. OxyMhr may either release O2, or undergo an autoxidation reaction in which hydrogen peroxide is released and diferric metMhr is produced. The autoxidation reaction can also be promoted by the addition of certain anions to Mhr solutions. This work, using recombinant Themiste zostericola Mhrs, contrasts the results of environmental effects on these reactions. For the O2 release reaction, ΔV(21.5°C)=+28±3 cm3 mol-1, ΔH(1 atm)=+22±1 kcal mol-1, and ΔS(1 atm)=+ 28±4 eu. The autoxidation reaction (pH 8.0, 21.5°C, 1 atm) displays different kinetic parameters: ΔV=-8±2 cm3 mol-1, ΔH=+24.1±0.7 kcal mol-1, and ΔS=+1±1 eu. Autoxidation in the presence of sodium azide is orders of magnitude faster than solvolytic autoxidation. The ΔV parameters for azide anation and azide-assisted autoxidation reaction are +15±2 and +59±2 cm3 mol-1, respectively, indicating that the rate-limiting steps for the Mhr autoxidation and anation reactions (including O2 uptake) are not associated with ligand binding to the Fe2 center. The L103V and L103N oxyMhr mutants autoxidize ≈ 103–105 times faster than the wild-type protein, emphasizing the importance of leucine-103, which may function as a protein ‘gate’ in stabilizing bound dioxygen.

Additional Information

The Journal of Inorganic Biochemistry 81:293-300 (2000).
Language: English
Date: 2000
Myohemerythrin, Autoxidation, Non-heme iron, Kinetics