To recapitulate, three non-homologous lyases have been examined, and despite their grouping into the same classification they vary greatly in both structure and mechanism. The lyases presented throughout this page correspond to distant evolutionary pathways, which is evidenced through their isolation from organisms from three separate kingdoms. Comparison of the individual folding topologies reveals three completely separate structures, encompassing: a TIM barrel, a single-stranded right handed ß-helix with a loop region, and an a/ß sandwich. Each unique folding topology results in unique active sites. In the Fructose-1,6-bisphosphate Aldolase the active site is at the center of the ß-barrel, in the Pectate Lyase it resides in the cleft formed between the ß-helix and the loop region, and in the C2 domain of the type II adenylyl cyclase the active site is formed by a cleft resulting from the interaction of the identical monomers. The mechanism each enzyme uses to carry out its given reaction varies from enzyme to enzyme. The FBPA forms a schiff-base intermediate which facilitates the carbon-carbon cleavage. The pectate lyase uses a calcium ion to alter the pka of an arginine residue, which than acts as a base for proton extraction in the elimination mechansim. The C2 domain must first interact with the C1a domain from optimal ATP binding. Once the ATP is bound, the 3' hydroxly group is deprotonated allowing it to undergo nucleophilic attack by the alpha-phosphate group.
Differences in these enzymes can also be observed through their locations in the cell. FBPA is found outside the mitochondria, while pectate lyase is found outside the cell entirely. The C2 domain is attached to the cell membrane on the cytostolic side. Despite the many differences in the enzymes they have been grouped together as lyases.