Anomalous Subdiffusion in Fluorescence Photobleaching Recovery: A Monte Carlo Study

Anomalous subdiffusion is hindered diffusion in which the mean-square displacement of a diffusing particle is proportional to some power of time less than one. Anomalous subdiffusion has been observed for a variety of lipids and proteins in the plasma membranes of a variety of cells. Fluorescence ph...

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Bibliographic Details
Published in:Biophysical journal 2001-10, Vol.81 (4), p.2226-2240
Main Author: Saxton, Michael J.
Format: Article
Language:English
Subjects:
Cells
Cellular biology
Diffusion
Fluorescence
Kinetics
Lipids
Membranes
Models, Chemical
Molecular Mimicry
Monte Carlo Method
Monte Carlo simulation
Photochemistry
Plasma
Proteins
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Summary:Anomalous subdiffusion is hindered diffusion in which the mean-square displacement of a diffusing particle is proportional to some power of time less than one. Anomalous subdiffusion has been observed for a variety of lipids and proteins in the plasma membranes of a variety of cells. Fluorescence photobleaching recovery experiments with anomalous subdiffusion are simulated to see how to analyze the data. It is useful to fit the recovery curve with both the usual recovery equation and the anomalous one, and to judge the goodness of fit on log-log plots. The simulations show that the simplest approximate treatment of anomalous subdiffusion usually gives good results. Three models of anomalous subdiffusion are considered: obstruction, fractional Brownian motion, and the continuous-time random walk. The models differ significantly in their behavior at short times and in their noise level. For obstructed diffusion the approach to the percolation threshold is marked by a large increase in noise, a broadening of the distribution of diffusion coefficients and anomalous subdiffusion exponents, and the expected abrupt decrease in the mobile fraction. The extreme fluctuations in the recovery curves at and near the percolation threshold result from extreme fluctuations in the geometry of the percolation cluster.
ISSN:0006-3495
1542-0086
DOI:10.1016/S0006-3495(01)75870-5