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The structure of TPI facilitates the conversion between dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP). The nucleophilic glutamate 165 residue of TPI deprotonates the substrate, [4] and the electrophilic histidine 95 residue donates a proton to form the enediol intermediate.
Triosephosphate isomerase is an enzyme that in humans is encoded by the TPI1 gene.. This gene encodes an enzyme, consisting of two identical proteins, which catalyzes the isomerization of glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP) in glycolysis and gluconeogenesis.
Thirteen different mutations in the respective gene, which is located at chromosome 12p13 and encodes the ubiquitous housekeeping enzyme triosephosphate isomerase (TPI), have been discovered so far. [4] TPI is a crucial enzyme of glycolysis and catalyzes the interconversion of dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.
Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GA3P, GADP, GAP, TP, GALP or PGAL, is a metabolite that occurs as an intermediate in several central pathways of all organisms. [2] [3] With the chemical formula H(O)CCH(OH)CH 2 OPO 3 2-, this anion is a monophosphate ester of ...
Step 5 in the figure is shown behind the other steps, because that step is a side-reaction that can decrease or increase the concentration of the intermediate glyceraldehyde-3-phosphate. That compound is converted to dihydroxyacetone phosphate by the enzyme triose phosphate isomerase, which is a catalytically perfect enzyme; its rate is so fast ...
The first reaction is the oxidation of glyceraldehyde 3-phosphate (G3P) at the position-1 (in the diagram it is shown as the 4th carbon from glycolysis), in which an aldehyde is converted into a carboxylic acid (ΔG°'=-50 kJ/mol (−12kcal/mol)) and NAD+ is simultaneously reduced endergonically to NADH.
Increased concentrations of DHAP and glyceraldehyde-3-phosphate in the liver drive the gluconeogenic pathway toward glucose-6-phosphate, glucose-1-phosphate and glycogen formation. It appears that fructose is a better substrate for glycogen synthesis than glucose and that glycogen replenishment takes precedence over triglyceride formation. [ 8 ]
The first substrate-level phosphorylation occurs after the conversion of 3-phosphoglyceraldehyde and Pi and NAD+ to 1,3-bisphosphoglycerate via glyceraldehyde 3-phosphate dehydrogenase. 1,3-bisphosphoglycerate is then dephosphorylated via phosphoglycerate kinase, producing 3-phosphoglycerate and ATP through a substrate-level phosphorylation.