Electron paramagnetic resonance studies and effects of vanadium in Saccharomyces cerevisiae

Vanadium uptake by whole cells and isolated cell walls of the yeast Saccharomyces cerevisiaewas studied. When orthovanadate was added to wild-type S. cerevisiaecells growing in rich medium, growth was inhibited as a function of the VO43-concentration and the growth was completely arrested at a concentration of 20 mM of VO43-in YEPD. Electron paramagnetic resonance (EPR) spectroscopy was used to obtain structural and dynamic information about the cell-associated paramagnetic vanadyl ion. The presence of EPR signals indicated that vanadate was reduced by whole cells to the vanadyl ion. On the contrary, no EPR signals were detected after interaction of vanadate with isolated cell walls. A ‘mobile’ and an ‘immobile’ species associated in cells with small chelates and with macromolecular sites, respectively, were identified. The value of rotational correlation time τrindicated the relative motional freedom at the macromolecular site. A strongly ‘immobilized’ vanadyl species bound to polar sites mainly through coulombic attractions was detected after interaction of VO2+ions with isolated cell walls.