The aggregation of alpha-synuclein is a hallmark feature of Parkinson's disease (PD) and other synucleinopathies. Metals are the significant etiological factors in PD, and their interaction with alpha-synuclein affect dramatically the kinetics of fibrillation in vitro and are proposed to play an important and potential neurodegenerative role in vivo. In the present study, we investigated the stoichiometry of binding of copper [Cu (II)] and iron [Fe (III)] with alpha-synuclein (wild recombinant type and A30P, A53T, E46K mutant forms) using isothermal titration calorimetry (ITC). alpha-Synuclein monomer (wild and mutant forms) titrated by Cu (II), showed two binding sites, with an apparent K(B) of 10(5)M and 10(4)M, respectively. But, alpha-synuclein (wild type and mutant forms) titrated with Fe (III) revealed a K(B) of 10(5)M with single binding site. The present investigation uncovers the detailed binding propensities between metals and alpha-synuclein and has biological implications in PD.