Branched-chain 2-oxo acid dehydrogenase interferes with the measurement of the activity and activity state of hepatic pyruvate dehydrogenase

Oxidative decarboxylation of pyruvate by branched-chain 2-oxo acid dehydrogenase can result in overestimation of the expressed and total activity of hepatic pyruvate dehydrogenase. Pyruvate is a poor substrate for branched-chain 2-oxo acid dehydrogenase relative to the branched-chain oxo acids; however, the comparable total activities of the two complexes in liver, the much greater activity state of branched-chain 2-oxo acid dehydrogenase compared with pyruvate dehydrogenase in most physiological states, and the use of high pyruvate concentrations, explain the interference that can occur in conventional radiochemical or indicator-enzyme linked assays of pyruvate dehydrogenase. Goat antibody that specifically inhibited branched-chain 2-oxo acid dehydrogenase was used in this study to provide a more specific assay for pyruvate dehydrogenase.