This is the matrix of the mitochondria, and this is the intermembrane space. Now, complex one is a very large complex. It's an L shaped multi subunit that contains about 46 individual polypeptide chains. So complex one is a very massive complex. Now, complex one is also known as NADH dehydrogenase or NADH oxidoreductase. And the reason we call it this is because this is the complex of the electron transport chain that ultimately accepts the high energy electrons from NADH molecules that we generate in processes such as the citric acid cycle and glycolysis.