ATP prevents G-actin cysteine oxidation and vanadyl formation specifically induced by decavanadate, suggesting that the oxometalate-protein interaction is affected by the nucleotide. The ATP exchange rate is increased by 2-fold due to the presence of decavanadate when compared with control actin (3.1 x 10(-3) s(-1)) and an apparent dissociation constant (k(dapp)) of 227.4 +/- 25.7 mu M and 112.3 +/- 8.7 mu M was obtained in absence or presence of 20 mu M V-10, respectively. Moreover, concentrations as low as 50 mu M of decameric vanadate species (V-10) increases the relative G-actin intrinsic fluorescence intensity by approximately 80% whereas for a 10-fold concentration of monomeric vanadate (V-1) no effects were observed. Upon decavanadate titration, it was observed a linear increase in G-actin hydrophobic surface (2.6-fold), while no changes were detected for V-1 (0-200 mu M). Taken together, three major ideas arise: i) ATP prevents decavanadate-induced G-actin cysteine oxidation and vanadate reduction; ii) decavanadate promotes actin conformational changes resulting on its inactivation, iii) decavanadate has an effect on actin ATP binding site. Once it is demonstrated that actin is a new potential target for decavanadate, being the ATP binding site a suitable site for decavanadate binding, it is proposed that some of the biological effects of vanadate can be, at least in part, explained by decavanadate interactions with actin. (C) 2010 Elsevier Inc. All rights reserved.