Final answer:
Activating pyruvate dehydrogenase kinase phosphorylates and inactivates E1 of the pyruvate dehydrogenase complex (PHD), reducing its activity and decreasing the rate of pyruvate metabolism.
Step-by-step explanation:
Pyruvate dehydrogenase kinase (PDH kinase or PDK) phosphorylates and inactivates E1 (pyruvate decarboxylase) of the pyruvate dehydrogenase complex (PHD). This phosphorylation prevents the conversion of pyruvate to acetyl-CoA, inhibiting the entry of pyruvate into the citric acid cycle. In other words, activating PDH kinase reduces the activity of E1 of PHD and decreases the rate of pyruvate metabolism.