Figure 2. ATP production rate and energy conversion efficiency.

(A) Steady-state ATP production rate, $k_{\mathrm{ATP}}$, calculated according to Equation (20), and (B) energy conversion efficiency, ${\eta }_{\mathrm{ATP}}$, calculated according to Equation (21), of a chromatophore vesicle as a function of incident light intensity $\mathrm{\Phi }$. Solid curves correspond to the vesicle shown in Figure 1; dashed curves represent a similar vesicle with only a single cyt$b{c}_1$. The vertical lines denote the light intensities corresponding to (I) 3% of full sunlight (30 W/m²), a typical growth condition for purple bacteria, and (II) full sunlight (1 kW/m²), respectively. Thus, for light intensities typical for the habitat of purple bacteria (1–5% of full sunlight; shaded area) the energy conversion efficiency ${\eta }_{\mathrm{ATP}}$ of a chromatophore vesicle is between 0.12–0.04.

DOI: http://dx.doi.org/10.7554/eLife.09541.005