Anal Biochem. 2004 326, 225-33.
Tracking variations in nicotinamide cofactors extracted from cultured cells using capillary electrophoresis with multiphoton excitation of fluorescence
D. D. Wise, J. B. Shear
Nicotinamide cofactors play numerous roles in cellular metabolic and biosynthetic reactions and intracellular signaling events. Recently, nicotinamide cofactors have been implicated in the function of cellular biological clocks. To gain insight into the possible roles of nicotinamide cofactors in complex time-related events, we have developed a rapid and sensitive method for extraction of NAD(P)(H) from cultured cells, separation of analytes by capillary electrophoresis, and detection by multiphoton excitation of fluorescence. Extraction and quantitation steps have been systematically characterized for optimal pH, detergent, temperature, sonication, filtration, efficiency, accuracy, and reproducibility. The method is suitable for extractions at 2- to 3-h intervals over 1 day or more or as frequently as every hour for shorter durations. Natively fluorescent NAD(P)H are assayed directly, and nonfluorescent NAD(P) are enzymatically reduced to their fluorescent counterparts before analysis. The method yields accurate values for cellular NADP, NADPH, and total NAD(H) levels and relative information on cellular NADH concentration; modification of the procedure allows full quantitation of all relevant species. We conclude that these assays are more suitable than any yet published for tracking variations in nicotinamide cofactor levels over periods of 1 day or more.