In 2009, a crystal structure of acetoacetate decarboxylase from "Clostridium acetobutylicum" was solved, allowing Westheimer et al.'s proposal to be evaluated from a new perspective . From the crystal structure, researchers found that Lys 115 and Lys 116 are oriented in opposite directions and separated by 14.8 Å (Figure 3). This distance makes it unlikely that the positive charge of Lys116 is able to affect the pKa of Lys115. Instead through hydrogen bonds with Ser16 and Met210, Lys116 likely holds Lys115 into position in a hydrophobic pocket of the active site. This positioning disrupts the stability of the protonated ammonium cation of Lys115, suggesting that the perturbation of Lys115's pKa occurs through a 'desolvation effect'.