Copper (II) - HisAibGly complex and its superoxide dismutase activity.

The superoxide anion radical is a highly reactive toxic species produced during metabolic processes. Several copper (II) complexes with peptides are known to show superoxide dismutase (SOD) activity but those having a peptide with a non-natural amino acid are limited. The synthesis of HisAibGly peptide and its complexation with copper (II) ions has been reported. The interaction of the synthetic peptide with Cu(II) was studied by electron spray ionization-mass (ESI-MS), circular dichroism (CD), absorption (UV-Vis) and electron paramagnetic resonance (EPR) spectroscopic methods. The solution studies and species distribution were performed by both spectrophotometric and potentiometric methods. The studies were performed at 25 + 0.1 degrees C with constant ionic strength (micro = 0.1 M NaNO(3)) in aqueous solution using Bjerrum-Calvin's pH-titration technique as adopted by Irving and Rossotti for binary systems. The species distribution stidies indicated that the complexation occurred from 3-11 pH and a three nitrogen coordinated species predominates at 8-9 whereas a four nitrogen coordinated species was formed between pH 9-11. The copper-peptide complex was tested for SOD activity using xanthine-xanthine oxidase - nitroblue tetrazolium (NBT) methods.