Evolution of Enzymatic Activity in the Tautomerase Superfamily:  Mechanistic and Structural Consequences of the L8R Mutation in 4-Oxalocrotonate Tautomerase ^†^,^‡Poelarends, Gerrit J.; Almrud, Jeffrey J.; Serrano, Hector; Darty, Joseph E.; Johnson,, William H.; Hackert, Marvin L.; Whitman, Christian P. · Biochemistry · 2006