Figure 4.

In the Paijmans model, at a lower bulk ATP fraction, individual hexamers make a smaller cycle through phosphorylation state space. We track the number of phosphorylated threonine sites, n_T, and serine sites, n_S, in each individual hexamer for one simulated hour at different phases of the oscillation. In (A) and (G), the shaded regions indicate at which phase of the oscillation the hexamers were probed and in which panel the result is shown. (B–F) α_ATP = 100% (left column) and (H–L) α_ATP = 50% (right column) show histograms of the probability of finding a hexamer in a certain phosphorylation state, indicated by the color bar to the right of the right column. Arrows are proportional to the flux through the state the arrow originates from. Comparing states near the peak of the phosphorylation level (D and J), hexamers at α_ATP = 50% go through a smaller cycle compared to the situation at 100% ATP. Specifically, the majority of hexamers go through n_T = 4 or 5 at α_ATP = 100%, whereas at 50%, hexamers only reach n_T = 2 or 3. Furthermore, the ensemble is less synchronized near the trough of the phosphorylation levels, comparing (F) and (L). Results shown are averaged over 400 consecutive oscillation cycles. To see this figure in color, go online.