An analogous ligand of blue copper active sites : synthesis, electron spin resonance characteristics of its copper(II) complex, and role of proline residue.

In order to clarify a role of the proline residue at near cysteine and histidine positions of plastocyanin and azurin, N-mercaptoacetylglycyl-L-prolyl-L-histidine has been synthesized as an analogous ligand of blue copper sites and the spectroscopic properties of its Cu(II) complex compared with those of the N-mercaptoacetylglycylglycyl-L-histidine-Cu(II) complex. In the present tetrapeptide-Cu(II) complexes, the exchange of the glycine of the third position by the proline residue effects a red shift(80 nm) of the visible absorption and a decrease (192→75×10^?4cm^?1) of the copper hyperfine splitting. The introduction of proline residue induces a change of the complex geometry from D_4h to T_d symmetries.