Figure 18.6 A schematic representation of the pyruvate dehydrogenase complex. The transacetylase core (E₂) is shown in red, the pyruvate dehydrogenase component (E₁) in yellow, and the dihydrolipoyl dehydrogenase (E₃) in green. The number and type of subunits of each enzyme are given parenthetically. Each red ball represents a trimer of three E₂ subunits. Notice that each subunit consists of three domains: a lipoamide-binding domain, a small domain for interaction with E₃, and a large transacetylase catalytic domain. The transacetylase domain has three subunits, with one subunit depicted in red and the other two in white in the ribbon representation.