Bioenergetic alteration in gastrointestinal cancers: The good, the bad and the ugly

Figure 1 Illustration of the pathway of glucose metabolism. Glucose is taken up by cells and undergoes a series of reactions to convert it to pyruvate via the process of glycolysis. Pyruvate can then enter the tricarboxylic acid cycle in the mitochondria to produce energy, or it can be converted to lactate in the cytosol under anaerobic conditions. The key enzymes involved in these reactions are highlighted in pale-purple, and linked pathways are depicted in pale-green. The mitochondrial complexes that are critical for oxidative phosphorylation and adenosine triphosphate production are shown in pale-blue. GLUT: Glucose transporter; HK: Hexokinase; G6P: Glucose-6-phosphate; G6PI: Glucose-6-phosphate isomerase; F6P: Fructose-6-phosphate; NADPH: Nicotinamide adenine dinucleotide phosphate; PFK1: Phosphofructokinase-1; F2,6BP: Fructose-2,6-bisphosphate; PFKBP3: Fructose-2,6-biphosphatase 3; F1,6BP: Fructose-1,6-bisphosphate; G3P: Glyceraldehyde-3-phosphate; DHAP: Dihydroxyacetone phosphate; GAPDH: Glyceraldehyde 3-phosphate dehydrogenase; 1,3BPG: 1,3-bisphosphoglycerate; 3PG: 3-phosphoglycerate; PGK: Phosphoglycerate kinase; PGAM: Phosphoglycerate mutase; 2PG: 2-phosphoglycerate; ENO: Enolase; PEP: Phosphoenolpyruvate; PKM1/2: Pyruvate kinase isozyme M1/M2; LDH: Lactate dehydrogenase; MCT: Monocarboxylate transporter family; PDH: Pyruvate dehydrogenase; IDH: Isocitrate dehydrogenase; α-KG: α-ketoglutarate; OAA: Oxaloacetate; SDH: Succinate dehydrogenase; FH: Fumarate hydratase; I: Mitochondrial complex I; II: Mitochondrial complex II; III: Mitochondrial complex III; IV: Mitochondrial complex IV; V: Mitochondrial complex V; Q: Co-enzyme Q; cyto C: Cytochrome c; ATP: Adenosine triphosphate; ADP: Adenosine diphosphate; FADH2: Flavin adenine dinucleotide; e^-: Electrons.