Proline, glucose and glycerol metabolism of the PCF trypanosomes.

Panel A shows a schematic representation of the proline metabolism (blue) in PCF grown in glucose-depleted medium, with glycerol contribution possibly present in the medium (black for the glycerol-specific steps). Panel B corresponds to cells incubated in glucose-rich medium, with contribution of glucose to central carbon metabolism indicated in red. End products excreted from catabolism of proline and glucose are shown in a rectangle, the number corresponding to enzymes under investigation are circled and metabolites analysed by IC-MS/MS are underlined and in italic. For the sake of clarity, the reversible non-oxidative branch of the pentose phosphate pathway (PPP) is represented by double lines and neither the glycerol 3-phosphate (Gly3P)/dihydroxyacetone phosphate (DHAP) shuttle nor the cofactors and nucleotides are shown. Abbreviations: DHAP, dihydroxyacetone phosphate; F1,6BP, fructose 1,6-bisphosphate; 1,3BPG, 1,3-bisphosphoglycerate; F6P, fructose 6-phosphate; G3P, glyceraldehyde 3-phosphate; G6P, glucose 6-phosphate; Gly3P, glycerol 3-phosphate; 6PG, 6-phosphogluconolactone; M6P, mannose 6-phosphate; OAA, oxaloacetate; PEP, phosphoenolpyruvate; 2PG, 2-phosphoglycerate; 3PG, 3-phosphoglycerate; Pen5P, pentose 5-phosphate (ribulose 5-phosphate, ribose 5-phosphate and xylose 5-phosphate). Indicated enzymes are: 1, proline dehydrogenase; 2, pyrroline-5 carboxylate dehydrogenase; 3, L-alanine aminotransferase; 4, α-ketoglutarate dehydrogenase complex; 5, succinyl-CoA synthetase; 6a, succinate dehydrogenase (complex II of the respiratory chain); 6b, mitochondrial NADH-dependent fumarate reductase; 7, mitochondrial fumarase; 8, mitochondrial malic enzyme; 9, pyruvate dehydrogenase complex; 10, acetate:succinate CoA-transferase (ASCT); 11, acetyl-CoA thioesterase; 12, cytosolic malic enzyme; 13, cytosolic fumarase; 14, glycosomal NADH-dependent fumarate reductase; 15, glycosomal malate dehydrogenase; 16, phosphoenolpyruvate carboxykinase (PEPCK); 17, pyruvate phosphate dikinase (PPDK); 18, pyruvate kinase; 19, enolase (ENO); 20, phosphoglycerate mutase; 21, cytosolic phosphoglycerate kinase; 22, glyceraldehyde-3-phosphate dehydrogenase; 23, triose-phosphate isomerase (TIM); 24, aldolase; 25, fructose-1,6-bisphosphatase (FBPase); 26, phosphofructokinase; 27, glucose-6-phosphate isomerase; 28, glucose-6-phosphate dehydrogenase (G6PDH); 29, 6-phosphogluconolactonase, 6-phosphogluconate dehydrogenase, ribose-5-phosphate isomerase and ribulose-5-phosphate epimerase; 30, phosphomannose isomerase; 31, hexokinase; 32, glycerol kinase (GK); 33, NADH-dependent glycerol-3-phosphate dehydrogenase (GPDH).