Labeling Studies in Isolated Mitochondria The metabolic pathways of organic compounds have often been delineated by using a radioactively labeled substrate and following the fate of the label. (a) How can you determine whether glucose added to a suspension of isolated mitochondria is metabolized to CO and HO? (b) Suppose you add a brief pulse of [3-4C] pyruvate (labeled in the methyl position) to the mito- chondria. After one turn of the citric acid cycle, what is the location of the 4C in the oxaloac- etate? Explain by tracing the 4C label through the pathway. How many turns of the cycle are required to release all the [3-4C] pyruvate as CO?