Quantification of intracellular NADPH levels
NADPH levels were quantified using the high sensitivity NADPH quantification fluorometric Assay Kit (#MAK216; Sigma Aldrich), as previously described [32]. The fluorescent reaction product was quantified with a SpectraMax i3X microplate reader (Molecular Devices, Sunnyvale, CA) using excitation and emission wavelengths of 535 and 587 nm, respectively.