Callahan & Miller (2007) summarize ODCase mechanisms in three proposals. The first one is the substrate carboxyl activation through electrostatic stress. The phosphoryl group binding entails juxtaposition between the carboxylate group and a negatively charged Asp residue (namely Asp91 in Saccharomyces cerevisae). Repulsion between the negative charges would raise the energy value near the transition state. Nonetheless, crystallographic analyses and the lack of S. cerevisae enzyme affinity to substrate analogues where the carboxylate groups is replaced by a cationic sustituent have shown some evidence against this theory.