Direct electrochemical regeneration of NADH from NAD⁺ using cholesterol-modified gold amalgam electrode

The efficiency of the direct electrochemical regeneration of NADH from NAD⁺ was enhanced by applying a cholesterol-modified gold amalgam electrode. The modified electrode was prepared by immersing gold plate in mercury and casting few drops of cholesteryl oleate solution over the gold amalgam. Coenzymatically active NADH was formed from NAD⁺ directly at the cholesterol-modified gold amalgam electrode which is supposed to hinder the dimerization of the NAD radicals on its membrane surface. The direct electrochemical NAD⁺ reduction process was used favorably to drive an enzymatic reduction of pyruvate to D-lactate. D-Lactate of 18.2 mm was obtained from pyruvate of 25.3 mm at 21 h of total reaction time in the electrolysis of 50 cm³ solution with the electrode of 6 cm²area. The turnover number for NAD⁺ was estimated as 1400.