Structural Features and Biological Functions in Blue Copper Proteins

A new idea that elucidates the electron carrier ability of plastocyanin (and o f azurin) is proposed. It emphasizes the fact that two lobes of the d-orbital. where one unpaired electron of copper (II) ion lies, are not screened by the ligand atoms, which would facilitate the electron transfer between the d-orbital and the redox partners (cytochrom e/ and P-700 in the case of plastocyanin). Several evidences which support the above proposal are provided. plastocyanin. and the tensor axis of gz is nearly paral­ lel to the Cu-S (thioether) bonding. The present au­ thor would like to point out that the electron transfer ability of plastocyanin can be closely related to the fact that two lobes of the dz : orbital are not screened by the ligand atoms (see below); so that the