FIGURE 3.
Comparison of chemical structures of dicarboxylate substrates, products, and inhibitors of complex II. Fumarate and succinate are the natural dicarboxylate substrates and products of complex II homologs. The remaining small molecules are demonstrated to be inhibitors. Inhibition of complex II by any of these small molecules, except citrate, is associated with neurodegenerative symptoms in humans or in animal models, and malate and 3-nitropropionate are commonly used in animal models of Huntington disease (25, 26). This figure was originally published in Ref. 32.