Effect of tyrosine residues on complexing of copper(II) by sulfhydryl-containing tripeptides: Its implication for tyrosine residues in blue copper proteins

A new tyrosine-containing sulfur-peptide, N-mercaptoacetyl-l-tyrosine (MAGT), was synthesized and its tyrosine effect on complex formation with Cu(II) investigated by electronic, circular dichroism (CD), fluorescence, and electron spin resonance (esr) spectra. The 1:1 MAGT-Cu(II) complex showed the following spectroscopic data: 545 nm (absorption maximum), 310 nm, 340 nm, and 580 nm (CD extrema), 280 nm and 308 nm (fluorescence peaks), and g_∥ = 2.17, g_⊥ = 2.05, A_∥ = 199.2 G, and A_N = 14.3 G (esr parameters). The tyrosine residue is near to but not directly bound to the Cu(II) in the MAGt complex. The present result has been discussed with respect to the role of tyrosine residues in blue copper proteins.