## 3 Results  
### pFBA Implementation to Define the Core Pathway from Glucose to Tyyptophan  
Implementing the pFBA algorithm defined 76 reactions as producing tryptophan, starting from D-glucose as optima reactions. Interestingly, the pathways described correspond with the proposed anthranilate growth-coupled production, with phosphoenolpyruvate and pyruvate as the key metabolites [17]. Highly connected metabolites and transport reactions for tryptophan and D-glucose were identified but not included in Figure 2 to facilitate their visualization.  
Figure 2: The pFBA identified 76 optima reactions as the shorter pathway with the minimal number  
number of reactions to produce tryptophan from glucose in the iML1515a GEM. Rectangles highlight the reactions, with color codes indicating the associated pathway: glycolysis (orange), the Krebs cycle (green), the non-oxidative (purple) and oxidative (light blue) phases of the pentose phosphate pathway, glutamine (pink), L-serine (brown), shikimate (gray), chobrismate (yellow), L-tryptophan (red), and others (white). The abbreviations in the figure are as follows: D-tructose 6-phosphate (F6P), D-tructose 1,6-biphosphate (F1,6 BP), glyceraldehyde 3-phosphate (G3P), dihydroxyacetone phosphate (DHAP), 3-Phospho-D-glyceroyl phosphate (1,3 DFG), 3-Phospho-D-glycerate (3 PG), D-glycerate 2-phosphate (2 PG), phosphoenolpyruvate (PEP), 2-oxoglutarate (AKG), succinyl-CoA (Suc-CoA), oxaloacetate (OAA), D-glucose 6-phosphate (G6P), 6-phospho-D-glucono-1,5-lactone (6 PGL), 6-Phospho-D-gluconate (6 PG), D-Ribulose 5-phosphate (Ru5P), D-xylulose 5-phosphate (Xu5P), \(\alpha\)-D-ribose 5-phosphate (R5P), D-erythrose 4-phosphate (E4P), sedoheptulose 7-phosphate (SH7P), sedoheptulose 1,7-bisphosphate (S1,7 BP), 5-phospho-alpha-D-ribose 1-diphosphate (PRPP), 3-phosphohydroxypruvate (3 PHP), O-phospho-L-serine (SOP), 2-dehydro-3-deoxy-D-arabino-heptonate 7-phosphate (DAHP), 3-dehydroquinate (DHQ), 3-dehydrooshikimate (DHS), shikimate 5-phosphate (SSP), 5-O-(1-carboxyvinyl)-3-phosphhiximate (CVPS), N-(5-phospho-D-ribosyl)anthrilate (PRAI), 1-(2-carboxyphenylamino)-1-deoxy-D-ribulose 5-phosphate (CDRP), C\({}^{\prime}\)-(3-indol)-glycerol 3-phosphate (IGP), xylose isomerase (XYLI2), hexokinase (HEX7), phosphofractokinase (PFK), phosphoglycerate mutase (PGM), enolase (ENO), phosphoenolpyruvate synthase (PPS), pyruvate dehydrogenase (PDH), citrate synthase (CS), aconitase A (ACONTa), aconitase B (ACONTb), isocitrate dehydrogenase (ICDHyr), 2-oxogluterate dehydrogenase (AKGDH), succinyl-CoA synthetase (SUCOAS), succinate dehydrogenase (SUCDji), fumarase (FUM), malate dehydrogenase (MDH), glucose-6-phosphate isomerase (PGI), fructose-bisphosphate aldolase (FBA), triose-phosphate isomerase (TPI), glucose 6-phosphate dehydrogenase (G6 PDH2r), 6-phosphogluconolactone (PGL), phosphogluconate dehydrogenase (GND), ribose-5-phosphate isomerase (RPI), ribulose 5-phosphate 3-epiemarse (RPE), transketolase 1 (TKT1), transketolase 2 (TKT2), sedoheptulose 1,7-bisphosphate D-glyceraldehyde-3-phosphate-lyase (FBA3), phosphofractokinase (SH7P) (PFK_3), glutamate dehydrogenase (GLUDy), glutamine synthetase (GLNS), phosphoribosylpyrophosph synthetase (PRPS), phosphoglycerate dehydrogenase (PGCD), phosphoserine transaminase (PSERT), phosphoserine phosphatase (PSP_L), 3-deoxy-D-arabino-heptulosonate 7-phosphate synthetase (DDPA), 3-dehydroquinate synthase (DHQS), 3-dehydroquinate dehydratase (DHQTi), shikimate dehydrogenase (SHK3 Dr), shikimate kinase (SHKK), 3-phosphhiximate 1-carboxyvinyltransferase (PSCVT), chorismate synthase (CHORS), anthranilate synthase (ANS), anthranilate phosphoribosyltransferase (ANPRT), phosphoribosylanthranilate isomerase (PRAli), indole-3-glycerol-phosphate synthase (IGPS), tryptophan synthase (IGP) (TRPS3), and tryptophan synthase (indole) (TRPS2).