An example of using fragment independence to obtain new isotopomer constraints under uniform substrate labelling. Constraints to the isotopomer distributions of striped metabolites are assumed to be known, either by direct measurement of measurement propagation. In pathway q = (ρ2, ρ4), the isotopomer distribution of M
molecules will be the same as in M
. In pathway p = (ρ1, ρ3), the isotopomer distribution of M
can be derived by applying fragment independence: the isotopomer distributions of single carbon metabolites produced by ρ1 are known a priori to be equal to the labelling degree of uniformly labelled substrate. As the two carbons of MF 3are produced from two different metabolites, these carbons are statistically independent to each other in the subpool and the isotopomer distribution D() of M
molecules produced by p can be computed by applying Equation 7.