Cytoplasmic viscosity

The effects of cytoplasmic viscosity are widely unexplored. This may be attributed to the relatively difficult measurement methods available. In the cytoplasm, magnetic microparticles were predominantly used to obtain information on viscoelastic properties [125-127]. Clearly, the use of magnetic microparticles demands the use of very expensive equipment the observation of the particles is time-consuming, thus limiting temporal resolution, and the interaction between the particles and the cellular environment may also cause measurement artifacts. 

This is a technological constraint, where the summation covers all enzyme fluxes (z in number, 30 in our case), nref is the i reference enzymatic reaction rate given in Table 13.1. Total enzymatic activity is constrained not to exceed 1.0 to avoid diffusion problem (due to increased cytoplasm viscosity), protein precipitation, secondary kinetic effects (due to steric hindrance) and excessive intracellular stress leading to unpredictable regulatory effects. When either one of these two constraints is breached, the objective function value is penalized by setting it to an arbitrarily low level under such conditions, the DAHPS, PEPCxylase and SerSynth fluxes are set to 10 °. 

Cytoplasmic viscosity A measure of the resistance of the cytosol to flow. (Units 1 Pa sec = 10 poise)... 

Power law fluid A model to describe the dependence of the cytoplasmic viscosity on rate of deformation (Equation 60.12). 

Needham, D. and Hochmuth, R.M. 1990. Rapid flow of passive neutrophils into a 4 /xm pipet and measurement of cytoplasmic viscosity. /. Biomech. Eng. 112 269-276. 

Some authors have worked with labelled proteins in solution. Kitevski-LeBlanc and co-workers prepared a sample of calmodulin enriched with 3-fluorophenylalanine. They reported CPMG dispersion experiments in order to characterize a transition to a thermal folding intermediate. Ye et worked with two other fluorine-labelled amino-acids and used F relaxation experiments to measure cytoplasmic viscosity and to characterize nonspecific protein-protein interaction in living cells. Yue and co-workers reported F relaxation data for a fluorocarbon covalently conjugated to albumin via flexible linkers. 

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