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Structural effects in alkyl nitrite oxidation of human hemoglobin
The Journal of Biological Chemistry
|January 10, 1984
Summary
Structural variations in alkyl nitrites significantly impact hemoglobin oxidation rates. These findings reveal insights into electron transfer mechanisms and hemoglobin
Area of Science:
- Biochemistry
- Chemical Kinetics
Background:
- Hemoglobin (Hb) undergoes oxidation, a process critical for its function and implicated in various pathologies.
- Alkyl nitrites are known to interact with heme proteins, but their detailed oxidative mechanisms with hemoglobin are not fully elucidated.
Purpose of the Study:
- To kinetically characterize the oxidation of oxyhemoglobin and deoxyhemoglobin by a series of structurally diverse alkyl nitrites.
- To elucidate the structural determinants influencing the rate and mechanism of these oxidation reactions.
- To investigate the role of hemoglobin's conformational states (R and T) in alkyl nitrite-mediated oxidation.
Main Methods:
- Kinetic analysis of hemoglobin oxidation by 10 different alkyl nitrites under varying oxygenation states.
- Temperature-dependent kinetic studies to determine activation parameters (activation energy, free energy of activation).
- Spectroscopic investigation to identify reaction intermediates and products, including the role of sulfhydryl groups.
Main Results:
- Significant structural influences on oxidation rate constants were observed, with rates spanning a 80-fold range.
- tert-Butyl nitrite exhibited the slowest oxidation rate, with incomplete oxidation of deoxyhemoglobin.
- Activation parameters revealed differences in free energies of activation between the R and T states of hemoglobin (1.8–2.9 kcal/mol).
- A sulfhydryl-induced oxidation pathway was identified, particularly pronounced in oxygen-saturated hemoglobin, attributed to nitrosyl exchange with cysteine residues.
Conclusions:
- Alkyl nitrite oxidation of hemoglobin proceeds via inner sphere electron transfer mechanisms.
- The kinetics of these reactions are directly influenced by the ligand-binding properties and conformational states of hemoglobin.
- The identified sulfhydryl-mediated pathway highlights a specific interaction between alkyl nitrites and hemoglobin's cysteine residues, affecting oxidative processes.