FIGURE 5.

Fits of the computed single-cell acceptor-box/donor-box ratio (Eq. 22) as a function of time (solid curves) to corresponding fluorescence intensity data (points) for (A) Alexa 350, (B) Alexa 488, and (C) Alexa 594. Calculations are based on the refined mesh. Parameter values are marked beside each computed curve. D_cyt is the cytoplasmic diffusivity; k_cyt and K_cyt^eq are the forward rate constant and equilibrium constant, respectively, for dye binding to the cytoplasm; and BG accounts for background signal resulting from any initially uniformly distributed dye, as well as autofluorescence and/or light refraction. For each dye, the parameter values listed in Table 1 represent averages of the values belonging to the individual curves (see text). The dashed curve in B represents a calculation in which binding of dye to the cytoplasm has been artificially suppressed by setting k_cyt = 0 (the value of K_cyt^eq is then immaterial). Its divergence from the experimental data demonstrates the importance of including binding in the model. Similar no-binding curves yield the same conclusion for the other dyes, but they are omitted in A and C to avoid clutter. Execution times required to generate these curves with one of our two Fortran codes, compiled with an Absoft Pro Fortran 7.0 F77 compiler (Absoft, Rochester Hills, MI) and run on an 850-MHz Pentium III notebook PC, range from ∼6 h (upper curve in A) to 16 h (solid curve in B).