Key Words enolase, amidohydrolase, thiyl radical, crotonase, (β/α)-barrels s Abstract The protein sequence and structure databases are now sufficiently representative that strategies nature uses to evolve new catalytic functions can be identified. Groups of divergently related enzymes whose members catalyze different reactions but share a common partial reaction, intermediate, or transition state (mechanistically diverse superfamilies) have been discovered, including the enolase,

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... thiyl radical, crotonase, vicinal-oxygen-chelate, and Fe-dependent oxidase superfamilies. Other groups of divergently related enzymes whose members catalyze different overall reactions that do not share a common mechanistic strategy (functionally distinct suprafamilies) have also been identified: (a) functionally distinct suprafamilies whose members catalyze successive transformations in the tryptophan and histidine biosynthetic pathways and (b) functionally distinct suprafamilies whose members catalyze different reactions in different metabolic pathways.