plasts and functions as an electron carrier from cytochrome f to P7OO in the electron transport chain between photosystem II and I.3) The redox reaction of plastocyanin is due to its copper valency change

Plastocyanin, a copper protein, was first isolated by Katoh in 1960 from the green alga, Chlorella ellipsoidea, and subsequently from various higher plants.l~,2) The protein is present in the chloroplasts and functions as an electron carrier from cytochrome f to P7OO in the electron transport chain between photosystem II and I.3) The redox reaction of plastocyanin is due to its copper valency change Cu ++ + e±Cu+. The cupric form shows a characteristic absorption band around 597 nm and two broad bands around 460 and 775 nm so that the color is bright blue. The cuprous form does not show any visible absorption. Plastocyanin is not autoxidizable and has a high midpoint redox potential of 0.37 volt.4> Structural analysis of plastocyanin indicates that this protein with about 10,000 molecular weight consists of single polypeptide chain of 98-105 amino acid residues and one copper atom.5~ The amino acid sequence of the protein from several higher plants has been investigated from a view point of molecular evolution.5~ Recently, the three dimensional structure has been determined for the poplar plastocyaninn by its X-ray analysis to be able to discuss about its inner-molecular mechanism of the electron transport activity of the protein.6~ We have been interested in comparative studies of the relationship between the physiological function and chemical properties or the structure, and molecular phylogeny of the photosynthetic electron carrier proteins, namely, algal cytochrome c6 and its analogous protein, plastocyanin.7~-°~ In this communication we wish to describe