were soluble, catalytically active, and were kinetically and structurally characterized. These chimeras have 5, 4 and 1 amino acid substitutions, respectively, as shown in Table . The final Chimera 7 carries a single amino acid substitution F182Q. This residue is adjacent to the general acid; previous work has hypothesized that the reorientation of the peptide bond joining these residues affects the energy barrier for loop movement.