TY - JOUR TI - Overall energy conversion efficiency of a photosynthetic vesicle AU - Sener, Melih AU - Strumpfer, Johan AU - Singharoy, Abhishek AU - Hunter, C Neil AU - Schulten, Klaus A2 - Hummer, Gerhard VL - 5 PY - 2016 DA - 2016/08/26 SP - e09541 C1 - eLife 2016;5:e09541 DO - 10.7554/eLife.09541 UR - https://doi.org/10.7554/eLife.09541 AB - The chromatophore of purple bacteria is an intracellular spherical vesicle that exists in numerous copies in the cell and that efficiently converts sunlight into ATP synthesis, operating typically under low light conditions. Building on an atomic-level structural model of a low-light-adapted chromatophore vesicle from Rhodobacter sphaeroides, we investigate the cooperation between more than a hundred protein complexes in the vesicle. The steady-state ATP production rate as a function of incident light intensity is determined after identifying quinol turnover at the cytochrome bc1 complex (cytb⁢c1) as rate limiting and assuming that the quinone/quinol pool of about 900 molecules acts in a quasi-stationary state. For an illumination condition equivalent to 1% of full sunlight, the vesicle exhibits an ATP production rate of 82 ATP molecules/s. The energy conversion efficiency of ATP synthesis at illuminations corresponding to 1%–5% of full sunlight is calculated to be 0.12–0.04, respectively. The vesicle stoichiometry, evolutionarily adapted to the low light intensities in the habitat of purple bacteria, is suboptimal for steady-state ATP turnover for the benefit of protection against over-illumination. KW - bacterial photosynthesis KW - excitation transfer KW - ATP production KW - energy conversion efficiency KW - Rhodobacter sphaeroides JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -