Effect of sodium on Saccharomyces cerevisiae invertase activity

Effect of Na+ ions on yeast invertase activity has been studied as a function of pH. At acidic pH, Na+ (5-100 mM) had no effect but invertase activity was inhibited (38-44%) by Na+ ions (100 mM) with an increase in pH (6.8 and 8.0). Kinetic analysis revealed that invertase inhibition by Na+ ions was non-competitive and reversible in nature. Value of K(m) remained unaltered (33.3 mM) in presence of Na+ (20-100 mM) while Vmax decreased by 21-44% under these conditions. Value of Ki was of the order of 85 mM. Mechanism of observed inhibition of invertase activity as a consequence of Na+ ions interactions at the active site of the enzyme has been described.