Strategy to estimate relative flux through major catabolic pathways. To completely resolve the contribution of each route, theoretical mass distributions of the [M-57] and [M-85] fragments of alanine were compared to the experimental data. In this schematic illustration, white circles represent unlabelled (12C) carbon whereas black circles indicate labelled (13C) carbon. The numbers given reflect the position of the carbon atom within the molecule. EDP: Entner-Doudoroff pathway; EMP: Embden-Meyerhof-Parnas pathway; PPP: pentose phosphate pathway.