Figure 8. Pauses primarily affected by clustering but skips primarily sensitive to available binding pockets.

Reactive spheres were simulated with S = 50 s⁻¹, R = 4.9 µm, n_L° = 90 sites/µm², 1×n_R° = 95 sites/µm², conditions similar to the experiment of Park et al. [23]. Association kinetics were governed by (1) or (2). The catch-slip dissociation model, (4), was used employing parameters regressed from the flow-cell data of Marshall et al. [5],[32] for dimeric interactions. Increased valency, V, was achieved for each receptor cluster site by using reliability theory rules [52] to create load-sharing molecular clusters. Therefore, 2×V might physically correspond to a tetrameric bond cluster. The black lines show the fit parameters reported in Table S1 and the dots show data points from the simulation. The percentile, “P,” indicates the uniform order statistic median. Each data set was pooled from three 10 s simulation runs. Blue: single valence receptor clusters with contact patch confinement. Red: single valence receptor clusters with molecular area confinement. Dark blue: double-valence receptor clusters with contact patch confinement. Maroon: double-valence receptor clusters with molecular area confinement. Green: single valence receptor clusters but with double the receptor cluster site density and contact patch confinement. Gold: single valence receptor clusters but with double the receptor cluster site density and molecular area confinement. (A) Non-transformed pause time data. (B) Non-transformed skip distance data. (C) Linear transform for Poisson-distributed pause times. (D) Linear transform for Poisson-distributed skip distances shows two distinct regions.