“…This means that a change in availability from substrate Sx to substrate Sy can lead to the adaptation of an organism by replacing enzyme Ex by Ey. Such adaptations have been studied experimentally for bacteria (519)(520)(521)(522)(523)(524). Successful examples are the evolution of an acetamidase to a phenylacetamidase (521) and of a ribitol dehydrogenase to a xylitol dehydrogenase (508,522).…”