... al. [12] todescribe l-carnithine biosynthesis with E. coli as hoststrain. Using the same modular model set-up, a clearrelationship between external cAMP and l-carnithinebiosynthesis was predicted ... twocontributions discussed here. This requires that thebalance equation be converted because, in cellular sys-tems, the reference value, the biomass, is also subjectto change. This results in a dilution ... models that represent completecells. This means that only subsystems of cells can beanalysed, which can lead to severe problems in thesuitability of a model. This is especially true for arational...