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Related Concept Videos

Photosystems01:32

Photosystems

7.7K
Photosystems are multiprotein complexes that form the functional units of photosynthesis in plants, algae, and cyanobacteria. They are found embedded in the membrane of tiny sac-like structures called thylakoids placed inside the chloroplast.
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment...
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The Antenna Complex01:15

The Antenna Complex

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Plants and other photosynthetic organisms comprise pigments capable of absorption of direct sunlight. These pigments are present in the reaction center - the main site of photochemical reactions as well as in the antenna complex. Under average light conditions, the rate at which reaction center pigments absorb light is far below the electron transport chain's capacity. As a result, the reaction center alone cannot provide enough energy to drive photosynthesis. The photosynthetic efficiency can...
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Photosystem II01:22

Photosystem II

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The multi-protein complex photosystem II (PS II) harvests photons and transfers their energy through its bound pigments to its reaction center, and ultimately to photosystem I (PSI) through the electron transport chain. The pigments responsible for caputirng the light energy in photosystems include chlorophyll a, chlorophyll b, and carotenoids.
The pigment molecules are arranged across  two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment...
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The Photochemical Reaction Center01:29

The Photochemical Reaction Center

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Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center is a more appropriate term that describes these complexes. The Nobel laureates Robert Emerson and William Arnold provided the first experimental evidence of photochemical reaction centers by demonstrating the participation of nearly 2,500 chlorophyll molecules for the release of just one molecule of oxygen. Despite thousands of photosynthetic...
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The Z-Scheme of Electron Transport in Photosynthesis01:34

The Z-Scheme of Electron Transport in Photosynthesis

14.2K
The light reactions of photosynthesis assume a linear flow of electrons from water to NADP+. During this process, light energy drives the splitting of water molecules to produce oxygen. However, oxidation of water molecules is a thermodynamically unfavorable reaction and requires a strong oxidizing agent. This is accomplished by the first product of light reactions: oxidized P680 (or P680+), the most powerful oxidizing agent known in biology. The oxidized P680 that acquires an electron from the...
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Photosystem I01:27

Photosystem I

70.4K
Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
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Purification of Active Photosystem I-Light Harvesting Complex I from Plant Tissues
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Probing structure-function relationships in early events in photosynthesis using a chimeric photocomplex.

Kenji V P Nagashima1, Mai Sasaki2, Kanako Hashimoto3

  • 1Research Institute for Photobiological Hydrogen Production, Kanagawa University, Kanagawa 259-1293, Japan; wt503649bw@kanagawa-u.ac.jp ykimura@people.kobe-u.ac.jp wang@ml.ibaraki.ac.jp.

Proceedings of the National Academy of Sciences of the United States of America
|September 23, 2017
PubMed
Summary

Calcium ions (Ca2+) are crucial for the stability of the light-harvesting complex 1 (LH1) in *Thermochromatium tepidum*. Specific amino acid residues, including α-D49 and β-L46, are identified as key for Ca2+ binding in this thermophilic bacterium.

Keywords:
Ca bindingQy transitionThermochromatium tepidumlight harvestingphotosynthesis

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Spectroscopy

Background:

  • The core light-harvesting complex 1 (LH1) from *Thermochromatium tepidum* requires Ca2+ for thermal stability and its characteristic 915 nm absorption peak.
  • Understanding Ca2+ binding in LH1 is essential for elucidating energy transfer mechanisms in phototrophic bacteria.

Purpose of the Study:

  • To investigate the role of specific amino acid residues in the LH1 polypeptides of *T. tepidum* concerning Ca2+ binding.
  • To characterize the heterologously expressed *T. tepidum* LH1 complex in *Rhodobacter sphaeroides*.

Main Methods:

  • Construction of a genetic system for heterologous expression of the *T. tepidum* LH1 complex in an engineered *R. sphaeroides* mutant.
  • Site-directed mutagenesis of LH1 polypeptides.
  • Characterization of hybrid LH1-RC complexes using absorption, fluorescence excitation, and resonance Raman spectroscopy.

Main Results:

  • Heterologous expression of the *T. tepidum* wild-type LH1 complex in *R. sphaeroides* yielded functional complexes with characteristic absorption properties.
  • Spheroidene was incorporated into the *T. tepidum* LH1 complex.
  • Spectroscopic analysis identified α-D49, β-L46, and an α-polypeptide deletion at position 43 as critical for Ca2+ binding, while α-N50 is not involved.

Conclusions:

  • Specific amino acid residues within the *T. tepidum* LH1 complex are definitively identified as crucial for Ca2+ coordination.
  • These findings complement structural data and pinpoint the Ca2+ binding site within this essential antenna complex.