 In "Thermotoga maritima", domain 1 contains 7 α-helices in residues 1-93, including the His68 which is highly conserved and was previously thought to be the catalytic acid in the active site.More recent studies have posited that the His171 in domain 2, previously thought to be a catalytic base, may in fact be acting as the catalytic acid, at least in "Escherichia coli".Domain 2 is made up of residues 94-341, and contains 5 α-helices and the monomer’s only β-sheet.