SINCE ITS FOUNDATION IN THE early 1990s (Bailey, 1991) metabolic engineering has repeatedly demonstrated its outstanding property to quantitatively understand cell metabolism thus provid-ing a sound basis for target-oriented optimization of new production strains (Nielsen, 1998; 2001). Among all the dierent tools being developed for metabolic engineering, metabolic ux analysis (MFA)

has played a dominating role (Wiechert, 2001), and perhaps can be regarded as the core of metabolic engineering (Stephanopoulos, 1999)—even today.