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Homogeneous nucleation in sickle hemoglobin: stochastic measurements with a parallel method
Journal article   Open access   Peer reviewed

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

Z Cao and F A Ferrone
Biophysical journal, v 72(1), pp 343-352
Jan 1997
PMID: 8994619
url
https://doi.org/10.1016/S0006-3495(97)78673-9View
Published, Version of Record (VoR) Open

Abstract

Thermodynamics Hemoglobin, Sickle - chemistry Photolysis Stochastic Processes Light Spectrophotometry - instrumentation Calorimetry Scattering, Radiation Spectrophotometry - methods Kinetics Macromolecular Substances
The homogeneous nucleation rate for sickle hemoglobin polymerization has been measured for concentrations from 3.9 to 4.9 mM and temperatures from 13 degrees C to 35 degrees C by observing the stochastic fluctuations of the time to complete 10% of the reaction after photolysis of the carboxy derivative. To allow efficient data collection, a mesh was used to divide the photolysis beam into an array of smaller beams, which allowed parallel observation of about 100 different regions. Nucleation rates measured here are consistent with more restricted previously published data and, when combined with directly measured monomer addition rates, are consistent with previous analysis of progress curves. By describing these rates with equilibrium nucleation theory, the concentration of nuclei and hence their stability can be ascertained. Consequently, the chemical potential by which a monomer is attached to the polymer is determined. This attachment energy ranges from -6.6 to -8.0 kcal/mol between 15 degrees C and 35 degrees C. The enthalpic part of that chemical potential is found to be equal to the enthalpy determined by solubility measurements, as expected from thermodynamic considerations. The entropic portion of the contact chemical potential contributes from -21.4 to -8.7 kcal/mol. The vibrational chemical potential of monomers in the polymer ranges from -25.7 to -27.4 kcal/mol over the same temperatures.

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Biophysics
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