Systems Biology Group, Max-Planck-Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany. kremling@mpi-magdeburg.mpg.de|Systems Biology Group, Max-Planck-Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany. kremling@mpi-magdeburg.mpg.de|Systems Biology Group, Max-Planck-Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany. kremling@mpi-magdeburg.mpg.de