Pathway Analysis of Optimal 13C Experiments. a) The maximum Z-score of all labeling patterns for each non-fixed reaction was found. Notably, greater than 50% of reactions have no experiment with a predicted Z-score greater than twice the noise level. This indicates that many reactions will be difficult to elucidate. b) Reactions separated by subsystem. Reactions with fluxes fixed by constraints are termed "constraint determined." The reactions with maximum Z-scores at least twice the noise level were termed "13C determinable." The difference between determinable/determined fluxes and 1 is the fraction of reactions that cannot be determined through either 13C experiments or constraints.