Functional evolution of photochemical energy transformations in oxygen-producing organisms

Abstract

Abstract. Chlorophyll a is the photochemical agent accounting for most oxygenic photosynthesis, that is, over 99.9% of photosynthetic primary activity on Earth. The spectral and energetic properties of chlorophyll a can, at least in part, be rationalised in terms of the solar spectral output and the energetics of oxygen production and carbon dioxide reduction with two photochemical reactions. The long wavelength limit on in vivo chlorophyll a absorption is probably close to the energetic limit: longer wavelengths could not support a high rate and efficiency of oxygenic photosynthesis. Retinal, a b-carotene derivative that is the chromophore of rhodopsin, acts not only as a sensory pigment, but also as an ion-pumping photochemical transducer. Both sensory and energy-transforming rhodopsins occur in oxygenic phototrophs, although the extent of expression and the function of the latter are not well understood.

Marine diatom proteorhodopsins and their potential role in coping with low iron availability

“…In ironlimited diatoms, 50-100% of the cellular iron requirement is within components of the photosynthetic electron carriers (Raven et al, 1999;Strzepek and Harrison, 2004). Therefore, the use of PR, which requires substantially less iron than photosynthesis, for ATP production would be advantageous under such conditions and is consistent with these findings as well as those hypothesized by others (Raven, 2009).…”

Comparative metatranscriptomics identifies molecular bases for the physiological responses of phytoplankton to varying iron availability

“…2). In comparing the energy and N costs between oxygenic photosynthesis and rhodopsins for photon absorption and the energized products formed, Raven (49) suggested there are few situations where photochemical generation of ion gradients and ATP by rhodopsins would be selectively favored. Due to the high iron requirements in oxygenic photosynthesis and lack of trace metals required in rhodopsins, one of these situations was suggested to be in low-iron environments, which is consistent with our findings (49).…”

Urea and nickel utilization in marine cyanobacteria as evaluated by incubation, proteomic, and uptake techniques

“…The critical role of iron in metalloenzymes amidst iron-limited growth conditions is known and leads to prospective shifts in enzyme selection in order to economize on iron [15], [16]. In more elaborate ways metalloenzymes may even routinely deconstructed and refabricated enzymes in order to separate diurnal processes and further economize for iron [10].…”