RUTHENIUM COMPLEXES AS REDOX MEDIATORS FOR MALATE AND LACTATE-DEHYDROGENASES

Two ruthenium complexes [Ru(phendione)(3)](2+) and [Ru(tpy) (bpy)H2O](2+) were tested as redox mediators for the electrocatalytic enzyme-coupled oxidation of malate and lactate with their respective dehydrogenase enzymes. Both complexes were capable of regenerating NAD(+) after its enzymatic reduction, but with varying current density as shown by cyclic voltammetry. Studies were performed at different concentrations of NAD(+) and the mediator and with different number of enzyme units. The best experimental conditions were used in experiments with different substrate concentrations. The results were fitted to the Michaelis-Menten equation giving the following K-M and V-max values in carbonate buffer at pH 9.3. Lactate dehydrogenase (r = 0.9999): K-M = 9.784+/-1.163 mM; k(cat) = 3.819+/-0.104 s(-1). Malate dehydrogenase (r = 0.9999): K-M = 3.934+/-0.722 mM;k(cat) = 3.376+/-0.171 s(-1).