Many regulatory processes in the cell are based on the control of gene expression through the interaction of transcription factors. However, enzymatic regulation often overlays transcriptional regulation and even, in some metabolic pathways, enzymatic regulation prevails. The present study addresses the regulatory network of Escherichia coli and offers a global view of the regulation of its metabolic pathways. It identifies the regulatory mechanisms responsible for key metabolic activities and details the structures behind such mechanisms. This knowledge is considered of relevance to further studies on the bacteria???s system and its industrial application, namely for understanding the signal cascades comprised in the responses to various environmental stresses. ; FCT funded MIT-Portugal Program in Bioengineering (MIT-Pt/BSBB/ 0082/2008); PhD grants from FCT (ref. SFRH/BD/22863/2005 and SFRH/BD/41763/2007).