Examples of sub-networks. a. Michaelis-Menten style enzyme, with a single enzyme-substrate complex, Yj, and reversible product formation, as in (5). b. Example with two enzyme-substrate complexes, Yj, Yk, leading irreversibly to Sv, along with a dead-end complex Ym. c. Example used in [41], with a single enzyme-substrate complex Yj and multiple products Sp, Sv, Sw. d. Alternative network to c with a different enzyme-substrate complex for each product. e. Example with partially overlapping routes for different products. f. Cyclic network, which may not correspond to known biochemistry but is mathematically allowed.