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search Structure from PDB 3BQV.  Plastocyanin is a copper-
containing protein involved in electron-transfer. The protein is
monomeric, with a molecular weight around 10,500 Daltons, and 99
amino acids in most vascular plants. It is a member of the
plastocyanin family of copper-binding proteins.   In
photosynthesis, plastocyanin functions as an electron transfer
agent between cytochrome f of the cytochrome b6f complex from
photosystem II and P700+ from photosystem I. Cytochrome b6f
complex and P700+ are both membrane-bound proteins with exposed
residues on the lumen-side of the thylakoid membrane of
chloroplasts. Cytochrome f acts as an electron donor while P700+
accepts electrons from reduced plastocyanin.   The copper site
in plastocyanin, with the four amino acids that bind the metal
labelled  Plastocyanin was the first of the blue copper proteins
to be characterised by X-ray crystallography. The tertiary
structure is a beta-barrel — common in protei