FIGURE 1.

Reaction mechanism examples of increasing complexity used to demonstrate the application of the three computational rules for apparent forward/backward flux quotients: (a) General bidirectional multistep Michaelis-Menten mechanism for a unimolecular reaction S → P. (b) Sequential mechanism for a unimolecular reaction S → P with two cofactors T, Q not taken into account for isotopic labeling. (c) Sequential binding mechanism for a bimolecular reaction S + T → P. (d) Random binding mechanism for a bimolecular reaction S + T → P. (e) Random bi-bi reaction mechanism with multiple substrates and products S + T → P + Q. S, T are substrates, P, Q are products, E is free enzyme, and M_i, ES, ET, EST, and ESPQ are enzyme complexes. Shaded circles indicate the potentially labeled substrates and products.