Figure 15From: (Im)Perfect robustness and adaptation of metabolic networks subject to metabolic and gene-expression regulation: marrying control engineering with metabolic control analysisIllustration of the hierarchical supply–demand structure of the leucine biosynthetic pathway. a1 and b1 denote the synthesis and degradation of enzyme Leu1 (E1); a2 and b2 denote the synthesis and degradation of enzyme Leu2 (E2). s and d represent the supply and demand modules as shown in Figure 14.Back to article page