This is a Jmol presentation by Seyma Keskin, Dec 1st, 2004 (click on the "About" menu above for more info on Jmol).

ABSTRACT:
Glycolysis is the biochemical pathway by which glucose is converted to pyruvate with the generation of 2 ATP/mol of glucose providing E utilized by most cells. Triosephosphate Isomeraze catalyzes the 5th reaction of the glycolytic pathway. With the exception of TIM from Pycoccus woesei and Methanothermus fervidus which are homotetramers, in all other species so far studied, a dimer is the physiologically active species. Rabbit muscle TIM, a dimer of identical subunits with a molecular mass of 2x26.6 kDa was one of the 1st glycolytic enzymes to be purified. Three structures of apo rabbit muscle TIM have been determined named A1, A2 and B and refined to 1.5 A, 2.85 A and 2.25 A respectively. A1 and A2 contain two dimers in asymmetric unit. A monomer of rabbit muscle TIM has 248 aa residues, with Lys 13, His 95 and Glu 165 being the key residues responsible for the catalysis. the active site loop segment comprises residues Pro166 to Ala176. Usually the open conformation has been described as apo and the closed conformation described as holo structures of complexes with substrate analogues, phosphate containing ligands. The active site loop of Triosephosphate Isomerase exhibits a hinged-lid motion between two well defined conformations. The loop moves upto 8A upon swinging from open to closed conformation. The main catalytic residue Glu 165 is shifted by about 2A. In this fashion, bulk solvent is excluded from the active site and key residues are repositioned for catalysis.