<prompt> Answer this question truthfullyHow is pyruvate dehydrogenase regulated through positive feedback, and what factors are involved in this regulation?  <response>: <reason> Pyruvate dehydrogenase is regulated through positive feedback by ADP, Ca2, and an increased NADNADH ratio. These factors activate pyruvate dehydrogenase, leading to an increase in the conversion of pyruvate to acetyl-CoA. This regulation helps to ensure that the citric acid cycle is able to produce ATP efficiently, by increasing the activity of pyruvate dehydrogenase when there is a need for more ATP production. 