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What is Protein Viscosity?

Published in Protein Biophysics 2 mins read

Protein viscosity refers to the resistance of a protein solution to flow, fundamentally determined by the various interactions occurring between individual protein molecules within the solution.

Understanding Protein Viscosity

The viscosity of a protein solution is a crucial physical property that describes its internal friction or its opposition to deformation under shear stress. Unlike simple liquids where viscosity might depend solely on molecular size and shape, the viscosity of protein solutions is highly complex. It results from several types of interactions between protein molecules [4, 5]. These intricate interactions dictate how protein molecules move past one another and collectively contribute to the overall flow behavior of the solution.

Key Interactions Influencing Protein Viscosity

Among the diverse forces that govern protein interactions and, consequently, solution viscosity, electrostatic repulsion plays a particularly significant role.

  • Electrostatic Repulsion: This force, governed by Coulomb's law, is a major determinant of the overall solution property [6]. Because it is a long-range interaction, it significantly influences how protein molecules arrange themselves and interact over greater distances within the solution. Proteins carry charges on their surface, and these charges can repel each other, creating a resistance to their movement and packing, which increases the solution's viscosity.

While electrostatic repulsion is highlighted as a major factor, it is important to note that protein viscosity is a cumulative effect of various other molecular interactions, including:

  • Hydrophobic interactions: Attraction between non-polar regions of proteins.
  • Van der Waals forces: Weak, short-range attractive or repulsive forces between all atoms and molecules.
  • Hydrogen bonding: Interactions involving hydrogen atoms bonded to highly electronegative atoms.
  • Steric hindrance: Physical obstruction due to the size and shape of protein molecules.

These combined interactions, detailed in various scientific literature [as listed in Table 1, 6], contribute to the unique rheological profile of different protein solutions, impacting their behavior in diverse applications, from biopharmaceutical formulations to food processing.