Pyruvate dehydrogenase (PDH) is the first component enzyme of the pyruvate dehydrogenase complex (PDC). As a key regulator of tricarboxylic acid (TCA) cycle flux, the PDC catalyzes the conversion of pyruvate into acetyl-CoA and regulates the entry of glucose-carbons into the TCA cycle. PDC deficiency is one of the most common neurodegenerative disorders associated with abnormal mitochondrial metabolism. This colorimetric assay is based on pyruvate dehydrogenase-catalyzed oxidation of pyruvate, where the resulting NADH can then convert a nearly colorless probe to a colored product. The intensity of the colored product is proportional to the amount of PDH in the sample, exhibiting maximum absorbance at 440nm.