P[Kappa]a is not responsible for the improved activity. Hence, stabilization of an enediolate intermediate may be important for catalysis. In the second part of this work, the Chloroflexus aurantiacus J-10-fl heterohexameric 4-OT tautomerase was employed in random and rational directed evolution studies to introduce a CaaD activity. Genetic selection and a high throughput screening assay were used to identify mutants. Genetic selection was unsuccessful due to plasmid instability in the host strain. A small mutant library in the screening assay precluded the identification of any mutants with CaaD activity. Finally, rational design using structure-function relationships was investigated and a single mutant was discovered for hh4-OT that incorporated CaaD activity into the enzyme, the [alpha]L9R hh4-OT, this mutant has been characterized kinetically and the evolutionary implications for the tautomerase superfamily are described. / text