Conformational kinetics of triligated hemoglobin

Area of Science:

• Biophysics
• Biochemistry
• Physical Chemistry

Background:

• Hemoglobin (Hb) undergoes conformational changes between oxy (R) and deoxy (T) states.
• Understanding these transitions is crucial for elucidating Hb function and allosteric regulation.

Purpose of the Study:

• To accurately measure the rate constants for conformational transitions between R and T states of triligated carboxy-hemoglobin A.
• To analyze the influence of pH on these kinetic parameters.
• To investigate the structural basis of the transition state and allosteric effects.

Main Methods:

• Utilized modulated excitation technique with an improved apparatus.
• Employed a revised analytical procedure for data analysis.
• Measured kinetic rates at pH 6.5 and 7.0.

Main Results:

• Determined rate constants for R to T (kRT) and T to R (kTR) transitions at two pH values.
• Observed kRT = 1.2 x 10^3 s^-1 and kTR = 3.5 x 10^3 s^-1 at pH 6.5.
• Observed kRT = 1.0 x 10^3 s^-1 and kTR = 3.0 x 10^3 s^-1 at pH 7.0.
• Found the equilibrium constant (L3) to be largely unchanged between pH 6.5 and 7.0.
• Identified a spectral feature near the HbCO Soret peak attributed to allosteric perturbation.

Conclusions:

• The transition state between Hb conformations is primarily governed by the deoxy (T) quaternary structure.
• Revised analytical methods reconcile current findings with previous data.
• Allosteric perturbations affect the spectral properties of liganded hemes.