Dielectric properties of insulin in solution

Area of Science:

• Biophysics
• Protein Chemistry
• Dielectric Spectroscopy

Background:

• Understanding protein hydration is crucial for comprehending protein structure, function, and interactions.
• Globular proteins vary in their surface hydrophilicity, influencing their water of hydration.
• Despentapeptide insulin (DPI) serves as a model to investigate hydration in proteins with potentially lower surface hydrophilicity.

Purpose of the Study:

• To determine the molecular volume and dipole moment of despentapeptide insulin (DPI) in solution using dielectric measurements.
• To quantify the water of hydration associated with DPI.
• To compare the hydration of DPI with other globular proteins.

Main Methods:

• Dielectric measurements of a 5% DPI solution across a frequency range of 0.2-50 MHz at six temperatures.
• Solvent composition: mixture of water and ethylene glycol at pH 3.
• Calculation of molecular volume by combining dielectric measurements with solvent viscosity data.

Main Results:

• The dipole moment of the insulin molecule was determined to be 72 +/- 1 at 25 degrees C.
• The molecular volume of DPI in solution was found to be only slightly larger than its crystalline volume.
• DPI exhibits a significantly lower quantity of water of hydration compared to globular proteins with more hydrophilic surface groups.

Conclusions:

• Despentapeptide insulin (DPI) has a compact structure in solution with minimal associated water.
• The low hydration of DPI suggests a relatively hydrophobic surface or specific packing arrangements.
• These findings contribute to the understanding of protein hydration and its relationship to surface properties.