'Rule of thumb' for time it takes a protein to diffuse across the cell

Value 0.5 sec
Organism Budding yeast Saccharomyces cerevisiae
Reference Calculated according to yeast cell diameter and average protein diameter. Please see Measurement Method
Method Taking X, distance to be traveled, as 4.5µm (BNID 100 451) and D in cytoplasm, as 10µm^2/sec (D in cytoplasm is in the range of 5-15µm^2/sec, GFP-BNID 100 193, 40kda dextran, similar weight to protein, BNID 100198). According to equation of diffusion (in 3 dimensions): t diffusion=X^2/(6×D). (4.5µm)^2/60µm^2/sec=0.338sec˜0.5sec.
Comments In cytoplasm there are solutes and D is smaller than in water (100µm^2/sec). D in water can be calculated from the Einstein-Stokes eq. D=KBT/6/p/?/R where R=2.5nm, typical protein radius. KB=Boltzmann's constant, ?=viscosity, 0.001 Pa×sec for water. (1.38×10^-23Kg×m^2×sec^-2×K^-1×300K)/ (6×3.14×0.001Kg×m^-1×sec^-1×2.5×10^-9m)= 8.8×10^-11m^2/sec=88µm^2sec˜100µm^2/sec
Entered by Uri M
ID 104525