Sandbox 143

Plastocyanin from a Green Alga, Enteromorpha prolifera

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OverviewOverview

Plastocyanin is an important copper-containing protein involved in photosynthesis by all higher plants and some algae namely by Enteromorpha prolifera. Plastocyanin extracted from this alga, was the first algal blue copper protein characterized by X-ray crystallography and one of the best characterized electron transfer protein of the photosynthetic apparatus. This protein was intensively studied between 1981 and 1994 because of these particular spectroscopic and electronic properties. The high resolution structural analysis by molecular replacement in 19891 provided an accurate description of the structure of this protein. Plastocyanin is an electron donor localized in the intern membrane of thylakoïd in chloroplast. This is a monomeric protein with a single polypeptide chain of 98 amino acids and one copper atom. The molecular weight of plastocyanin is around 10,500 Daltons.

Role in PhotosynthesisRole in Photosynthesis

ContextContext

In the sunlight reaction, in photosynthesis, the plastocyanin is an important electron donor to the Photosystem I (P700).Thanks to its hydrophobic surface, plastocyanin is localised in the intern membrane of the thylakoid in chloroplasts. Its redox potential, about 370 mV, has allowed to determine the place of plastocyanin in the electron transport chain (between the photosystem II to the photosystem I): between the cytochrome b₆f complex and the phtosystem I. Plastocyanin receive an electron from the cytochrome b₆f complex and give up its electron to the photosystem I.

Electron Transfer MechanismElectron Transfer Mechanism

The copper atom bound to the plastocyanin is in the shape Cu²⁺. This shape of plastocyanin is reduced by the cytochrome b₆f according to the following reaction : Cu²⁺Pc + e^- → Cu⁺Pc. The electron is given up by the cytochrome b₆f and transforms plastocyanin in shape Cu²⁺ into plastocyanin in shape Cu⁺. Then this plastocyanin diffuses through the lumen of thylakoid (remember its localisation in intern membrane of the thylakoid) until the recognition and binding occurs with the photosystem I.