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Mechanisms underlying carotenoid absorption in oxygenic photosynthetic proteins.

ABSTRACT: The electronic properties of carotenoid molecules underlie their multiple functions throughout biology, and tuning of these properties by their in vivo locus is of vital importance in a number of cases. This is exemplified by photosynthetic carotenoids, which perform both light-harvesting and photoprotective roles essential to the photosynthetic process. However, despite a large number of scientific studies performed in this field, the mechanism(s) used to modulate the electronic properties of carotenoids remain elusive. We have chosen two specific cases, the two ?-carotene molecules in photosystem II reaction centers and the two luteins in the major photosystem II light-harvesting complex, to investigate how such a tuning of their electronic structure may occur. Indeed, in each case, identical molecular species in the same protein are seen to exhibit different electronic properties (most notably, shifted absorption peaks). We assess which molecular parameters are responsible for this in vivo tuning process and attempt to assign it to specific molecular events imposed by their binding pockets.

SUBMITTER: Mendes-Pinto MM

PROVIDER: S-EPMC3696649 | biostudies-literature | 2013 Jun

REPOSITORIES: biostudies-literature

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Mechanisms underlying carotenoid absorption in oxygenic photosynthetic proteins.

Mendes-Pinto Maria M MM Galzerano Denise D Telfer Alison A Pascal Andrew A AA Robert Bruno B Ilioaia Cristian C

The Journal of biological chemistry 20130517 26

The electronic properties of carotenoid molecules underlie their multiple functions throughout biology, and tuning of these properties by their in vivo locus is of vital importance in a number of cases. This is exemplified by photosynthetic carotenoids, which perform both light-harvesting and photoprotective roles essential to the photosynthetic process. However, despite a large number of scientific studies performed in this field, the mechanism(s) used to modulate the electronic properties of c ...[more]

PMID: 23720734

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Project description:Red and blue light are traditionally believed to have a higher quantum yield of CO2 assimilation (QY, moles of CO2 assimilated per mole of photons) than green light, because green light is absorbed less efficiently. However, because of its lower absorptance, green light can penetrate deeper and excite chlorophyll deeper in leaves. We hypothesized that, at high photosynthetic photon flux density (PPFD), green light may achieve higher QY and net CO2 assimilation rate (A n) than red or blue light, because of its more uniform absorption throughtout leaves. To test the interactive effects of PPFD and light spectrum on photosynthesis, we measured leaf A n of "Green Tower" lettuce (Lactuca sativa) under red, blue, and green light, and combinations of those at PPFDs from 30 to 1,300 μmol⋅m-2⋅s-1. The electron transport rates (J) and the maximum Rubisco carboxylation rate (V c,max) at low (200 μmol⋅m-2⋅s-1) and high PPFD (1,000 μmol⋅m-2⋅s-1) were estimated from photosynthetic CO2 response curves. Both QY m,inc (maximum QY on incident PPFD basis) and J at low PPFD were higher under red light than under blue and green light. Factoring in light absorption, QY m,abs (the maximum QY on absorbed PPFD basis) under green and red light were both higher than under blue light, indicating that the low QY m,inc under green light was due to lower absorptance, while absorbed blue photons were used inherently least efficiently. At high PPFD, the QY inc [gross CO2 assimilation (A g)/incident PPFD] and J under red and green light were similar, and higher than under blue light, confirming our hypothesis. V c,max may not limit photosynthesis at a PPFD of 200 μmol m-2 s-1 and was largely unaffected by light spectrum at 1,000 μmol⋅m-2⋅s-1. A g and J under different spectra were positively correlated, suggesting that the interactive effect between light spectrum and PPFD on photosynthesis was due to effects on J. No interaction between the three colors of light was detected. In summary, at low PPFD, green light had the lowest photosynthetic efficiency because of its low absorptance. Contrary, at high PPFD, QY inc under green light was among the highest, likely resulting from more uniform distribution of green light in leaves.

Dataset Information

Mechanisms underlying carotenoid absorption in oxygenic photosynthetic proteins.

Publications

Mechanisms underlying carotenoid absorption in oxygenic photosynthetic proteins.

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