Figure 4.

Intensity distribution and stoichiometry of detected events. (a) Intensity distributions for events detected in simulated confocal images for either stationary particles with different brightness (left panel) or particles with brightness $B=20$ kHz and different diffusion coefficients. (b) Intensity distributions for events detected in confocal images of SLB incubated with tBid-Alexa647 and Bax-HyLite488, classified for each protein into stationary and mobile particles (regardless of Bax concentration). All intensities have been normalized by the known particle brightness of the monomer. The experimental distributions are binned in two different ways, with a small bin width of $B/4$ for visualization (orange bars) and with a larger bin width of B or $0.7B$ for stationary and mobile particles, respectively, representing the expected apparent brightness of a monomer for these two types of particles (blue bars). The coarse binning thus provides an estimate of the relative abundance of different protein stoichiometry. In (a,b), the dashed vertical bars indicate the threshold intensity used for particle detection. (c) Oligomer frequency versus Bax-HyLite488 concentration (for a constant $0.2$ nM tBid-Alexa647 concentration).