Coenzyme Models. 10. Rapid Oxidation of NADH by a Flavin Immobilized in Cationic Polyelectrolytes

The title flavin rapidly oxidizes NADH, the observed enhancement being of 460-4650-fold compared with 3-methyltetra-O-acetylriboflavin. Analysis of the kinetic data at 30 °C established that the reaction proceeds according to the Michaelis-Menten kinetics at low ionic strength (µ=0.02: Km=ca. 10-5 M, kcat=0.06-0.37 s-1) and according to the simple second-order kinetics at high ionic strength (µ=0.3), the largest rate difference being 342-fold. On the other hand, the oxidation of l-benzyl-l,4-dihydronicotinamide, a NADH model compound, was not accelerated by the use of the title flavin. It is concluded, therefore, that the formation of the polymeric flavin-NADH complexes due to the electrostatic interaction is responsible for the marked rate enhancement. This is the first example that the oxidation of NADH is facilitated in the nonenzymatic system.