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Diffusion coefficients of a protein as obtained from FCS measurements performed at different solvent viscosities.

Molecular crowding effects
The cellular cytoplasm is crowded with many different macromolecules reaching concentrations with hundreds of grams per liter. Hence, a substantial fraction (20-30%) of the total volume of any cell is occupied by macromolecules. This crowding increases the effective concentration of molecules and affects the physical properties of the solution (“excluded volume” effect). For example, molecular mobility and dynamics within constrained volumes are suppressed in the cytosol. As a consequence, molecular crowding decreases diffusion rates, shifts equilibria of protein-protein association and of protein-substrate interactions, and changes conformational dynamics of proteins. We have performed fluorescence correlation spectroscopy studies on several proteins dissolved in highly concentrated solutions of Ficoll (of different molecular weights ranging from 5-400 kDa), which mimics molecular crowding in biological cells.

Biophysics (Aachen):
Jörg Fitter

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