Enolase reaction catalyzed

Enolase catalyzes the conversion of 2-phosphoglycerate to phosphoenolpyrnvate + H9O. The standard free energy change, AG°, for this reaction is +1.8 kj/mol. If the concentration of 2-phosphoglycerate is 0.045 mM and the concentration of phosphoenolpyrnvate is 0.034 mM, what is AG, the free energy change for the enolase reaction, under these conditions ... 

The first interconversion between glycerate-3-phos-phate and glycerate-2-phosphate is similar to the reaction catalyzed by phosphoglucomutase (fig. 12.22). The enzyme is transiently phosphorylated in the course of the reaction. The second interconversion in the three-carbon pool is between glycerate-2-phosphate and phosphoenolpyruvate. This reaction is catalyzed by enolase and entails a dehydration (see fig. 12.13). 

The overall pathway is shown in Figure 13-1, and some properties of these reactions and the enzymes involved are listed in Table 13-2. Glycolytic enzymes can be classified into six groups according to the type of reaction catalyzed kinase, mutase, dehydrogenase, cleaving enzyme, isomerase, and enolase. 

Both the 1,1-proton transfer reaction catalyzed by mandelate racemase (MR) and the dehydration catalyzed by enolase require Mg + for activity. The values of the pK s for mandelate and 2-phosphoglycerate, the substrates for the MR- and enolase-catalyzed reactions, are estimated as 29 and 32, respectively [1]. The values of the pKaS of the general basic Lys residues are 6 and 9 in MR [6] and enolase [73], respectively. Thus, formation of a dienolate anion intermediate is extremely endergonic, unless the active site can stabilize the intermediate which is the obvious function of the essential Mg. The rate accelerations for the MR- and enolase-catalyzed reactions are 10 as a direct result of the values of the pKaS of the a-protons (Table 6.1). 

What is the role of NAD+ in a biochemical oxidation reaction Write the equation for the reaction catalyzed by glyceraldehyde-3-phosphate dehydrogenase. Highlight the chemical changes that show this to be an oxidation reaction. The enzyme that catalyzes step 9 of glycolysis is called enolase. What is the significance of that name ... 

The enzyme was overexpressed, purified to homogeneity, and its properties investigated. The enzyme required a divalent metal ion for activity like the other members of the enolase superfamily. The enzyme was shown to carry out the dehydration of SHCHC (15) to OSB (7) very efficiently with A(.at (19 Is ) and a (1.6 0.3 X 10 mol 1 s ). OSB synthase was classified as a member of the enolase superfamily. Members of this superfamily carry out reactions initiated by the abstraction of the a-proton from a carboxylate anion substrate to generate a stabilized enolate anion intermediate. As pointed out above, the reaction catalyzed by OSB synthase is a dehydration. It was proposed that the a-proton of the carboxylate substrate (SHCHC) is likely abstracted by a basic catalyst (one lysine) followed by the elimination of the /3-hydroxyl group presumably by the assistance of an acid catalyst (a second lysine). 

Phosphosulfolactate synthase (ComA), catalyzes the first step in coenzyme M biosynthesis (Figure 20), which is the stereospecific Michael addition of sulfite to phosphoenolpyruvate to form phosphosulfolactate as shown in Figure 23. On the basis of the reaction catalyzed, ComA was predicted to be related to the enolase superfamily of enzymes however, the overall structure and active-site architecture of ComA are unlike any member of the enolase superfamily. This suggests that ComA is not a member of the enolase superfamily but instead acquired an enolase-type mechanism through convergent evolution. ... 

Figure 15 Reactions catalyzed by members of the enolase superfamily. Reproduced with permission from J. A. Gerit P. C. Babbitt I. Payment, Arch. Biochem. Biophys. 2005, 433, 59-70.

Figure 17. (a) The reaction catalyzed by enolase, and (b) the proposed mechanism of action of the enzyme. 

The equilibrium constant of the enolase reaction is about 1 (omitting water from the equation). The equilibrium constant of the reaction catalyzed by phosphoglyceromutase is about 10, varying somewhat with temperature. Since these constants are small, it is apparent that the three phosphorylated 3-carbon acids are freely interconverted, and that at equilibrium most of the ester will be 3-PGA, but several per cent of each of the others will also be present. 

The enolase superfamily is now composed of at least 23 distinct proteins " of which functions have been experimentally verified for 11. The overall reactions catalyzed by the superfamily members of known function include racemization, epimerization, and both syn and anti elimination reactions involving substantially different substrates. While all of the substrates used by these enzymes contain a proton or to a car-boxylate group, none of the superfamily members is known to cross-react with the substrate of another family member. 

StepS 9-1° of F Sure 29-7 Dehydration and Dephosphorylation Like mos /3-hydroxy carbonyl compounds produced in aldol reactions, 2-phospho glvcerate undergoes a ready dehydration in step 9 by an ElcB mechanism (Section 23.3). The process is catalyzed by enolase, and the product i... 

Decarboxylases are one of the members of the enolase superfamily. The most important and interesting point of this class of enzymes is that they are mechanistically diverse and catalyze different overall reactions. However, each enzyme shares a partial reaction in which an active site base abstracts a proton to form a nucleophile. The intermediates are directed to different products in the different active sites of different members. However, some enzymes of this class exhibit catalytic promiscuity in their natural form. ° This fact is considered to be strongly related to the evolution of enzymes. Reflecting the similarity of the essential step of the total reaction, there are some successful examples of artificial-directed evolution of these enzymes to catalyze distinctly different chemical transformation. The changing of decarboxylase to racemase described in Section 2.5 is also one of these examples. 

Even an entirely different enzyme can be changed to the one that has enolase activity. One representative example is the changing of a lipase to an aldolase utilizing the basicity of the catalytic triad via a simple mutation. The resulting promiscuous lipase has been demonstrated to catalyze the aldol reaction and Michael addition as shown in Fig. 23. 

The Truhlar group has reported an interesting theoretical study of H/D kinetic isotope effects for conversion of 2 phospho-D-glycerate to phosophoenolpyruvate catalyzed by the yeast enolase enzyme. The proton transfer step (first reaction step in Fig. 11.10) is the rate limiting step and was chosen for theoretical study. The KIE for proton/deuteron transfer is kn/kD = 3.3 at 300 K. 

Enolase [EC 4.2.1.11] catalyzes the interconversion of 2-phosphoglycerate and phosphoenolpyruvate in a stepwise mechanism. Proton abstraction and at least one additional step (eg., hydroxide loss or product release) may limit the overall reaction rate. 

Enolase catalyzes the dehydration of 2-phosphoglycerate to form phospho-enolpyruvate (PEP). This reaction converts the low-energy phosphate ester bond of 2-phosphoglycerate into the high-energy phosphate bond of PEP. 

The enolase superfamily story started with the serendipitous discovery that two enzymes catalyzing very different overall reactions, mandelate racemase (MR) and muconate lactonizing enzyme (MLE), had virtually superimposable structures (Neidhart et al., 1990). As shown in Figure 2, MR catalyzes the reversible racemization of mandelate, an aromatic substrate, while MLE catalyzes the equilibration of muconolactone with as, m-muconate. Given the substantial differences in these reactions, it... 

Hatano, 1995b) from Amycolaptosis sp. is known to catalyze more than one different chemical reaction using a substantially different substrate (Palmer et al., 1999). Investigation of this catalytic flexibility in the context of the enolase superfamily raises the question of whether this enzyme may represent an example of nature s present-day reengineering of the superfamily scaffold for an entirely new function. Other examples of catalytically promiscuous enzymes from other superfamilies have been observed, as reviewed by O Brien and Herschlag (O Brien and Her-schlag, 1999). 

Dehy dration and dephoftphorylation. btke the J3-h> droxy carbonyl oin-potinds produced in aidol reactions. 2>phusphog ycerate undergoes a ready dehydration (Secticm 23-4 K The process is catalyzed by enolase. and the product is phosphoenolpyruvate, abbreviated PkIP. 

In the next reaction, an enol is formed by the dehydration of 2-phosphoglycerate. Enolase catalyzes the formation of phosphoenolpyruvate (PEP). This dehydration markedly elevates the transfer potential of the phosphoryl group. An enol phosphate has a high phosphoryl-transfer potential, whereas the phosphate ester, such as 2-phosphoglycerate, of an ordinary alcohol has a low one. The A G° of the hydrolysis of a phosphate ester of an ordinary alcohol is -3 kcal mofi (-13 kJ mol i), whereas that of phosphoenolpyruvate is -14.8 kcal mofi (- 62 kJ mofi). Why does phosphoenolpyruvate have such a high phosphoryl-transfer potential The phosphoryl group traps the molecule in its unstable enol form. 

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