Triosephosphate isomerase

An enzyme involved in glycolysis and gluconeogenesis

Triosephosphate isomerase

Triosephosphate isomerase (TPI, TIM) is an enzyme that plays a critical role in the metabolic pathways of glycolysis and gluconeogenesis. It catalyzes the reversible interconversion of the three-carbon sugars dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P). This reaction is essential for efficient energy production and utilization in cells.

Structure

Triosephosphate isomerase is a highly efficient enzyme with a structure that is often described as a "TIM barrel," a common protein fold consisting of eight _-helices and eight parallel _-strands that alternate along the peptide backbone. This structure is not only characteristic of TPI but is also found in many other enzymes, highlighting its evolutionary significance.

File:Triosephosphate isomerase structure.png

Structure of triosephosphate isomerase showing the TIM barrel fold.

Function

The primary function of triosephosphate isomerase is to catalyze the conversion between DHAP and G3P. This reaction is crucial in the glycolytic pathway, where it ensures that the energy yield from glucose metabolism is maximized. In the absence of TPI, DHAP would accumulate, and the efficiency of glycolysis would be significantly reduced.

Mechanism

The catalytic mechanism of TPI involves the formation of an enediol intermediate. The enzyme stabilizes this intermediate through precise positioning of amino acid residues in the active site, facilitating the conversion between DHAP and G3P. The reaction proceeds with remarkable speed and efficiency, making TPI one of the most "catalytically perfect" enzymes known.

Clinical significance

Deficiency in triosephosphate isomerase activity can lead to a rare genetic disorder known as triosephosphate isomerase deficiency. This condition is characterized by hemolytic anemia, neurological dysfunction, and increased susceptibility to infections. The deficiency is caused by mutations in the TPI1 gene, which encodes the enzyme.

Evolutionary significance

The TIM barrel structure of triosephosphate isomerase is one of the most common protein folds and is found in a wide variety of enzymes across different species. This suggests that the TIM barrel is a highly adaptable and efficient structural motif that has been conserved throughout evolution.

Related pages

• Glycolysis
• Gluconeogenesis
• Enzyme
• Metabolism
• Protein structure