Structural Biochemistry/Enzyme Catalytic Mechanism/Isomerases/Enzyme/Isomerases/Triose Phosphate Isomerase
'Triose Phosphate Isomerase' (TPI) is an isomerase that catalyzes the isomerization of dihydroxyacetone phosphate to and from D-glyceraldehyde 3-phosphate. It takes part in the glycolytic pathway, which is a biochemical pathway employed by many organisms. The objective of this pathway is to metabolize glucose into two pyruvate molecules, also producing two ATP molecules. Hence, TPI is an enzyme that contributes to the production of ATP, the molecules used as an energy source by all organisms.
TPI is an example of a "kinetically perfect enzyme," which means that it catalyzes isomerization so quickly that the rate of reaction is determined by the diffusion rate of the substrate. This means it isomerizes essentially every molecule of TPI specificity that it encounters. TPI increases the rate of isomerization by ten degrees of magnitude. Part of TPI's kinetical perfection comes from it being an isomerase; the enzyme does not have to wait for multiple substrates to bind to the active site. Also, the mechanism (see below) involves few steps and involves the transfer of protons only.