Triosephosphate isomerase, mechanism

Figure 3 A possible mechanism for the isomerization of dihydroxyacetone phosphate (DHAP) to D glyceraldehyde 3 phosphate (GAP) by the enzyme triosephosphate isomerase (TIM). The general acid (Glu 165) and general base (His 95) are shown.

Barton-Davis ER, Cordier L, Shotrrrma Dl, Leland SE, Sweeney HL (1999) Aminoglycoside antibiotics restore dystrophin function to skeletal muscles of mdx mice. J Clin Invest 104 375-381 Belgrader P, Cheng J, Maquat LE (1993) Evidence to implicate translation by ribosomes in the mechanism by which nonsense codons reduce the nuclear level of human triosephosphate isomerase mRNA. Proc Natl Acad Sci USA 90 482 86... 

In the Briggs-Maldane mechanism, when k2 is much greater than k-i, kcJKM is equal to kx, the rate constant for the association of enzyme and substrate. It is shown in Chapter 4 that association rate constants should be on the order of 108 s l M l. This leads to a diagnostic test for the Briggs-Haldane mechanism the value of kaJKu is about 107 to 108 s-1 M-1. Catalase, acetylcholinesterase, carbonic anhydrase, crotonase, fumarase, and triosephosphate isomerase all exhibit Briggs-Haldane kinetics by this criterion (see Chapter 4, Table 4.4). 

The interconversion of the two triosephosphates is an essential step in the catabolism of carbohydrates (see chapter 12). Examining the catalytic mechanism of triosephosphate isomerase is instructive. It is among the enzymes that ap-... 

The probable reaction mechanism of triosephosphate isomerase. The y-carboxylate group of Glu 165 acts as a general base to remove a proton from C-l of the substrate, dihydroxyacetone phosphate (DHAP). This generates a planar ene-diolate intermediate that has two... 

Lack of congruence of structure and mechanism Common structure does not imply a common mechanism The /1-barrel structures triosephosphate isomerase and xylose isomerase function by hydride transfer through enol, whereas aldose reductase performs hydride transfer through a metal ion. 

Dihydroxyacetone phosphate is converted to D-glyceraldehyde 3-phosphate by the enzyme triosephosphate isomerase as part of the glycolytic pathway of metabolism. Show how this interconversion could occur by a base-catalyzed mechanism ... 

Cui Q, M Karplus (2002) Quantum mechanics/molecular mechanics studies of triosephosphate isomerase-catalyzed reactions Effect of geometry and tunneling on proton-transfer rate constants. J. Am. Chem. Soc. 124 (12) 3093-3124... 

Compound V or glycidol phosphate was used by Rose and O Connell (1969) to study muscle triosephosphate isomerase because it closely resembles the presumed ene-diol intermediate in this enzyme s reaction mechanism. Coincidentally, it also proved to be an effective inhibitor of enolase even though it is not closely analogous to substrates of this enzyme. The structure of glycidol phosphate is similar to phosphononomycin (DC), an antibiotic isolated from fermentation broths of Streptomyces fradiae (Christensen et al. 1969). 

An enzyme that has been the subject of intensive experimental and theoretical studies is triosephosphate isomerase (TIM), which catalyses the interconversion of dihydroxyacetone phosphate (DHAP) and D-glyceraldehyde 3-phosphate (GAP), an essential step in the glycolytic pathway (Fersht 1985). The mechanism of the enzyme has been examined by QM/MM calculations which we do not describe here because it falls outside the topic ofthis review (Bash et al. 1991). However, an additional aspect of the overall mechanism is the conformational change of an 11-residue loop region (residues 166-176) which moves more than 7 A and closes over the active site when substrate binds (Joseph et al. 1990 Lolis et al. 1990). Mutagenesis experiments have... 

Enzyme mechanisms can often avoid high-energy, unstable cationic or anionic intermediates that increase the reaction barrier. Triosephosphate isomerase catalyzes the tautomerization of the achiral dihydroxy acetone phosphate (DHAP) to f -glyceraldehyde-3-phosphate (G3P) by the mechanism shown below. Not only does the push-pull mechanism avoid forming a highly basic enolate, but the binding mode of DHAP determines which face of the enediol will be protonated in the second step, and therefore... 

Normal mode analysis of the mechanical properties of a triosephosphate isomerase-barrel protein suggests that the region between the secondary structures plays an important role in the dynamics of the protein. The beta-barrel region at the core of the protein is found to be soft in contrast to the helical, strand and loop regions [62]. A detailed discussion of other properties of proteins is mechanically highly non-linear systems is given by Kharakoz [63]. 

Triosephosphate isomerase catalyzes the conversion of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate. The enzyme s catalytic groups are Glu 165 and His 95. In the first step of the reaction, these catalytic groups function as a general-base and a general-acid catalyst, respectively. Propose a mechanism for the reaction. 

List the reactions that convert fructose 1,6-bisphosphate, a hexose, into the triose glyc-eraldehyde 3-phosphate. Summarize the most important features of the catalytic mechanism of triosephosphate isomerase I. 

A number of studies on the metabolism of 3FG and 4FG in Locusta miaratoria have been undertaken. Both 3FG and 4FG are toxic to locust with LD50 s of 4.8 mg/g and 0.6 mg/g respectively. In vitro studies showed that 3FG is metabolized in the fat body, via the NADP-linked aldose reductase, to 3-deoxy-3-fluoro-D-glucitol (3FGL). This metabolite was detected in the hemolymph of the insect and shown to be both a competitive inhibitor and a substrate for NAD-linked sorbitol dehydrogenase, thereby generating 3-deoxy-3-fluoro-D-fructose (3FF) (541. Subsequently, it was shown by in vivo radio-respirometric analysis of C02 and appropriate chase experiments, that 3FG metabolism irreversibly inhibits glycolysis and not the hexose monophosphate shunt or tricarboxylic acid cycle (55). In addition, the release of fluoride ion and H20 from D-[3- H]-3FG was also observed. Based on the mechanism of aldolase (55) and triosephosphate isomerase... 

Triosephosphate isomerase, for example, catalyzes the interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate with fccat values that vary with pH, whereas is pH independent in the neutral range. This behavior appears consistent with mechanisms in which the enzyme combines with either monoanionic or dianionic forms of the substrate with similar affinity, but only the latter forms a productive complex, ES , which goes on to form products. Unlike an ordinary substrate analog, a transition-state analog for this reaction would be expected to be bound tightly only as a dianionic species, and this appears to be the case for the inhibitor 2-phosphoglycolic acid. ... 

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