We describe the development of a computational approach for the identification of every possible biochem. reaction from a given set of enzyme reaction rules that allows the de novo synthesis of metabolic pathways composed of these reactions, and the evaluation of these novel pathways with respect to their thermodn. properties. We applied this framework to the anal. of the arom. amino acid pathways and the central carbon metab. - glycolysis and pentose phosphate pathway. Thermodn. anal. of these pathways was used for the comparison of the native pathways with the alternative possible pathways. The pathways generated involve compds. that exist in biol. databases, as well as compds. that exist in chem. databases and novel compds., suggesting novel biochem. routes for these compds. and the existence of biochem. compds. that remain to be discovered or synthesized through enzyme and pathway engineering. [on SciFinder (R)]