Three-dimensional structure of the metabolic enzyme pyruvate dehydrogenase (PDH). Pyruvate dehydrogenase is the first component enzyme of pyruvate dehydrogenase complex. PDH turns pyruvate, which comes from sugar, into acetyl CoA. This is an important step in creating energy for the cell. An outer structure of E1 subunits (purple) surround a core of E2 subunits (green). One unit of catalytically active portions of PDH are shown in red, green, and yellow. Created by Donald Bliss (NLM) and Sriram Subramaniam, 2002.