In this work we investigated the formation of a complex between gamma-thionin SI alpha1 and Ca(2+) using differential pulse voltammetry and MALDI TOF/MS. A stoichiometry rate of one calcium ion per one SI alpha1 molecule was obtained. K(d) values of 1.31 x 10(-9) mol L(-1), 2.63 x 10(-8) mol L(-1) and 2.71 x 10(-8) mol L(-1) were determined for the Ca(2+)- SI alpha1 complex by three different methodologies. These findings contribute to a better understanding of the SI alpha1 inhibition mechanism towards insect and mammalian alpha-amylases.