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Triosephosphate isomerase
The structure of human TPI PDB 1WYI
Symbol TPI1
Entrez 7167
HUGO 12009
RefSeq NM_000365
Other data
EC number
Locus Chr. 12 p13

Triose-phosphate isomerase (TPI or TIM), is an enzyme (EC that catalyzes the reversible interconversion of the triose phosphate isomers dihydroxyacetone phosphate and D-glyceraldehyde 3-phosphate.

Side view of triose P isomerase monomer, active site at top center
Dihydroxyacetone phosphate triose phosphate isomerase D-glyceraldehyde 3-phosphate
Glycerone-phosphate wpmp.png   D-glyceraldehyde-3-phosphate wpmp.png
Biochem reaction arrow reversible NNNN horiz med.png
  triose phosphate isomerase

Compound C00111 at KEGG Pathway Database.Enzyme at KEGG Pathway Database.Compound C00118 at KEGG Pathway Database.

TPI plays an important role in glycolysis and is essential for efficient energy production. TPI has been found in nearly every organism searched for the enzyme, including animals such as mammals and insects as well as in fungi, plants and bacteria. However, some bacteria that do not perform glycolysis, like ureaplasmas, lack TPI.

In humans, deficiencies in TPI are associated with a progressive, severe neurological disorder called triose phosphate isomerase deficiency.

Triose phosphate isomerase is a highly efficient enzyme, performing the reaction billions of times faster than it would occur naturally in solution. The reaction is so efficient that it is said to be catalytically perfect: it is limited only by the rate the substrate can diffuse into the enzyme's active site.



The mechanism involves the intermediate formation of an "enediol". The changes in free energy for each step, including the transition states, have been calculated, and are displayed in the figure.[1]

Free energy changes

Side view of triose phosphate isomerase dimer.


Triose phosphate isomerase is a dimer of identical subunits, each of which is made up of about 250 amino acid residues. The three-dimensional structure of a subunit contains eight α-helices on the outside and eight parallel β-strands on the inside. In the illustration, the ribbon backbone of each subunit is colored in blue to red from N-terminus to C-terminus. This structural motif is called an αβ-barrel, or a TIM-barrel, and is by far the most commonly observed protein fold. The active site of this enzyme is in the center of the barrel. A glutamic acid residue as well as a histidine are involved in the catalytic mechanism. The sequence around the active site residues is conserved in all known triose phosphate isomerases.

See also


  1. ^ Albery, W. J.; Knowles, J. R. (1976). "Free-Energy Profile for the Reaction Catalyzed by Triosephosphate Isomerase". Biochemistry 15 (25): 5627–5631. doi:10.1021/bi00670a031. PMID 999838.  




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