Blue copper binding proteins are prevalent in all forms of life, yet most of them have not been functionally identified. These proteins have special folding characteristics, which allow them to bind a single copper atom, a co-factor responsible for their unique redox characteristics. Because copper is a transition metal with a 3d configuration, it can accept or give a single electron, changing its oxidation state from +2 (3d<sup>9</sup>) to +1 (3d<sup>10</sup>). This property makes blue copper proteins excellent candidates for electron transfer in biological systems. This report focuses on two closely related blue copper proteins - chemocyanin from Lilium longiflorum and plantacyanin from Arabidopsis thaliana . These proteins have been classified as blue copper proteins, primarily based on the sequence features commonly found in the amino acid sequences of the other members in this family. However, they have neither been purified nor characterized biochemically. On the other hand, it has been recently established that lily chemocyanin induces a chemotropic effect which is manifested by guiding the pollen to the ovary, through a newly developed pollen tube during plant fertilization (Kim et. al., 2003). After purifying these copper binding proteins, we will test their biophysical properties, in particular we will determine their redox potentials. This will provide us with important information which we can use to gain insight in the function and pathways of chemocyanin and plantacyanin in plant chemotropism.