System state fluctuations caused by enzyme deletions. The impacts of enzyme deletions on system states are shown. In all subfigures, x-axis: state variable (metabolite) indexes (denoted as "Metab", see Additional file 6 for details); y-axis: distance of state variable from the deleted enzyme ("Dist"); z-axis: the impact amplitude ("Amp"). (A - D) The influences of TKb, PGK, TIS, and PGI deletions on system state, respectively. The figures exemplify that an enzyme can affect distant metabolites even greater than its closest neighbours.