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The electron transport protein plastocyanin is present in the lumen and shuttles electrons from the cytochrome b6f protein complex to photosystem I. While plastoquinones are lipid-soluble and therefore move within the thylakoid membrane, plastocyanin moves through the thylakoid lumen.
Photosystem I [1] is an integral membrane protein complex that uses light energy to catalyze the transfer of electrons across the thylakoid membrane from plastocyanin to ferredoxin. Ultimately, the electrons that are transferred by Photosystem I are used to produce the moderate-energy hydrogen carrier NADPH . [ 2 ]
Reaction centers are multi-protein complexes found within the thylakoid membrane. At the heart of a photosystem lies the reaction center, which is an enzyme that uses light to reduce and oxidize molecules (give off and take up electrons). This reaction center is surrounded by light-harvesting complexes that enhance the absorption of light.
Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants , algae , and cyanobacteria .
The gradient is only used to power transport across the thylakoid membrane, however, while the gradient in the mitochondria is used to power transport across its inner membrane. [3] Furthermore, due to the thylakoid membrane located inside of the chloroplast, a second transit peptide sequence must be located on the imported protein.
In contrast to the Sec pathway which transports proteins in an unfolded manner, the Tat pathway serves to actively translocate folded proteins across a lipid membrane bilayer. In plants, the Tat translocase is located in the thylakoid membrane of the chloroplast , where it acts to export proteins into the thylakoid lumen.
The light-harvesting complex (or antenna complex; LH or LHC) is an array of protein and chlorophyll molecules embedded in the thylakoid membrane of plants and cyanobacteria, which transfer light energy to one chlorophyll a molecule at the reaction center of a photosystem. The antenna pigments are predominantly chlorophyll b, xanthophylls, and ...
For instance, in chloroplasts during photosynthesis, an electron transport chain pumps H + ions (protons) in the stroma (fluid) through the thylakoid membrane to the thylakoid spaces. The stored energy is used to photophosphorylate ADP, making ATP, as protons move through ATP synthase.