Short-lived intermediates in hemoglobin/O2 systems

Area of Science:

• Biophysical Chemistry
• Chemical Kinetics
• Molecular Biophysics

Background:

• Hemoglobin's reaction with oxygen is crucial for physiological respiration.
• Understanding the precise kinetic mechanisms of oxygen binding to hemoglobin is complex.
• Previous studies have utilized rapid mixing techniques to probe hemoglobin kinetics.

Purpose of the Study:

• To numerically simulate and analyze the kinetics of hemoglobin-oxygen reactions.
• To investigate the feasibility of distinguishing between four proposed kinetic mechanisms.
• To determine the experimental conditions required for mechanistic discrimination.

Main Methods:

• Numerical simulation of hemoglobin-oxygen reaction kinetics.
• Application of rapid mixing followed by a temperature jump (T-jump) technique.
• Analysis of chemical relaxation phenomena at various time scales.

Main Results:

• Four distinct kinetic mechanisms for hemoglobin-oxygen binding were modeled.
• Discrimination between mechanisms is challenging at low oxygen concentrations (<100 microM).
• Distinguishing mechanisms requires high resolution in time and concentration amplitude at higher oxygen levels.
• Differences in molar extinction coefficients are critical for experimental validation.

Conclusions:

• Chemical relaxation kinetics, combined with T-jump, can resolve reaction steps not detectable by rapid mixing alone.
• Experimental distinction between proposed hemoglobin-oxygen binding mechanisms is possible in principle.
• Precise experimental conditions and component molar extinction coefficients are essential for successful discrimination.