 The exact mechanism used by sulfotransferases is still being elucidated, but studies have indicated that sulfotransferases use an in-line sulfonyl-transfer mechanism that is analogous to the phosphoryl transfer mechanism used by many kinases, which is logical given the great level of structural and functional similarities between kinases and sulfotransferases (Figure 2).In carbohydrate sulfotransferases a conserved lysine has been identified in the active PAPS binding site, which is analogous to a conserved lysine in the active ATP binding site of kinases.Protein sequence alignment studies indicate that this lysine is conserved in cytosolic sulfotransferases as well.