Plastocyanin/azurin family of copper-binding proteins (or blue (type 1) copper domain) is a
family of small proteins that bind a single copper atom and that are characterised by an intense electronic absorption band near 600 nm (see
copper proteins). The most well-known members of this class of proteins are the plant chloroplastic
plastocyanins, which exchange electrons with
cytochrome c6, and the distantly related bacterial
azurins, which exchange electrons with cytochrome c551. This family of proteins also includes
amicyanin from bacteria such as
Methylobacterium extorquens or
Paracoccus versutus (Thiobacillus versutus) that can grow on methylamine; auracyanins A and B from
Chloroflexus aurantiacus; blue copper protein from
Alcaligenes faecalis; cupredoxin (CPC) from
Cucumis sativus (Cucumber) peelings; cusacyanin (basic blue protein; plantacyanin, CBP) from cucumber; halocyanin from
Natronomonas pharaonis (Natronobacterium pharaonis), a membrane-associated copper-binding protein; pseudoazurin from Pseudomonas;
rusticyanin from
Thiobacillus ferrooxidans; stellacyanin from
Rhus vernicifera (Japanese lacquer tree); umecyanin from the roots of
Armoracia rusticana (Horseradish); and allergen Ra3 from ragweed. This pollen protein has evolutary relation to the above proteins, but seems to have lost the ability to bind copper. Although there is an appreciable amount of divergence in the sequences of all these proteins, the copper ligand sites are conserved.