Homogeneous nucleation in sickle hemoglobin: stochastic measurements with a parallel method

Area of Science:

• Biophysics
• Thermodynamics
• Polymerization kinetics

Background:

• Sickle hemoglobin polymerization is central to sickle cell disease pathogenesis.
• Understanding nucleation is key to inhibiting polymerization.
• Previous studies lacked detailed nucleation rate data.

Purpose of the Study:

• To quantitatively measure homogeneous nucleation rates of sickle hemoglobin.
• To determine the chemical potential and stability of nuclei.
• To elucidate the thermodynamic driving forces of sickle hemoglobin polymerization.

Main Methods:

• Homogeneous nucleation rate measurements using photolysis of carboxy-hemoglobin.
• Parallel observation of ~100 regions using a mesh beam splitter.
• Application of equilibrium nucleation theory.

Main Results:

• Nucleation rates were measured across a range of concentrations (3.9-4.9 mM) and temperatures (13-35°C).
• Measured rates are consistent with existing data and analysis of progress curves.
• Attachment energy per monomer ranges from -6.6 to -8.0 kcal/mol.
• Entropic and vibrational contributions to chemical potential were quantified.

Conclusions:

• The study provides precise measurements of sickle hemoglobin nucleation rates.
• Equilibrium nucleation theory allows determination of nucleus stability and monomer attachment energy.
• Thermodynamic parameters, including enthalpy and entropy, are elucidated, offering insights into polymerization mechanisms.