Isomerases racemases

Many enzymes (especially isomerases, racemases, and epimerases) catalyze intramolecular reactions that can be described by a Uni Uni mechanism. These are typically written with one or two central complexes ... 

Isomerases Racemases Isomerases Catalyze inversions at asymmetric carbon atoms and the intramolecular transfer of molecular constituents. 

Isomerases Racemases Epimerases Isomerases Mutases Transfer of groups within a molecule to )deld isomeric forms A - B A - B i 1 1 i... 

Isomerases (racemases, epimerases, isomerases, mutases) Isomerization Disulphide isomerase EC5.3.4.1... 

Isotnerases. These catalyse the structural or geometric changes within a molecule. The division includes racemases, epimerases, cis-rran -isomerases, lautomerases and mulases. 

These catalysts facilitate the interconversion of isomeric compounds and include racemases, optimerases, cis-trans isomerases, intramolecular oxidoreductases and intramolecular transferases. Scheme 10.14 shows the conversion of an aldehyde to a ketone by triose phosphate isomerase. 

PROLINE REDUCTASE L-Proline to D-proline interconversion, PROLINE RACEMASE PROLIPOPROTEIN SIGNAL PEPTIDASE PROLYL 3-HYDROXYLASE PROLYL 4-HYDROXYLASE PROLYL ISOMERASE... 

TRIOSE-PHOSPHATE ISOMERASE AFFINITY LABELING HALDANE RELATION ENZYME ENERGETICS (The Case of Proline Racemase)... 

Figure 2.5 Logarithmic scale comparison of k,d and kuncat (= (rnon) for some representative reactions at 25 °C. The length of each vertical bar represents the rate enhancement. (Wolfenden, 2001). ADC arginine decarboxylase ODC orotidine 5 -phosphate decarboxylase STN staphylococcal nuclease GLU sweet potato /3-amylase FUM fumarase MAN mandelate racemase PEP carboxypeptodase B CDA E. coli cytidine deaminase KSI ketosteroid isomerase CMU chorismate mutase CAN carbonic anhydrase.

B major axis near /J-strand 1 M R, M LE are missing final a-helix domains cover the C-terminal end of the barrel domain blocks N-terminus of the barrel mandelate racemase, muconate cycloisomerase, xylose (glucose) isomerase... 

Class 5. Isomerases interconvert isomeric structures by intramolecular rearrangements. They include racemases, epimerases, cis- and trans-isomerases, intramolecular transferases (mutases), and intermolecular lyases. 

Relatively little is known about applications of this class of enzymes. In general, they catalyze geometric or structural changes within one molecule. According to the type of isomerization effected, they may be called racemases, epimerases, (cis-trans) isomerases, and tautomerases. Currently, about 126 isomerases are known, of which only about six are available commercially. 

The isomerase class of biocatalysts represents a small number of enzymes that are mainly composed of the racemases, epimerases, and mutases. In the case of racemases and epimerases, the stereochemistry of at least one carbon center is changed, while mutases catalyze the transfer of a functional group, such as an amino function, to an adjacent carbon, forming a new stereocenter. One of the... 

Isomerases catalyze intramolecular rearrangements and are subdivided into racemases, epimerases, mutases, cis-trans-isomerases, etc. examples glucose isomerase (EC 5.3.1.5)... 

The glycolytic pathway includes three such reactions glucose 6-phosphate isomer-ase (1,2-proton transfer), triose phosphate isomerase (1,2-proton transfer), and eno-lase (yS-elimination/dehydration). The tricarboxylic acid cycle includes four citrate synthase (Claisen condensation), aconitase (j5-elimination/dehydration followed by yS-addition/hydration), succinate dehydrogenase (hydride transfer initiated by a-proton abstraction), and fumarase (j5-elimination/dehydration). Many more reactions are found in diverse catabolic and anabolic pathways. Some enzyme-catalyzed proton abstraction reactions are facilitated by organic cofactors, e.g., pyridoxal phosphate-dependent enzymes such as amino acid racemases and transaminases and flavin cofactor-dependent enzymes such as acyl-C-A dehydrogenases others. 

As first espoused by Knowles and Albery, the limiting selective pressure on enzymatic function is the diffusion-controlled limit by which substrates bind and products dissociate [7]. In the case of triose phosphate isomerase [8], ketosteroid iso-merase [9], mandelate racemase [10], and proline racemase [11], the energies of various transition states on the reactions coordinates have been quantitated, with the result that the free energies of the transition states for the proton transfer reactions to and from carbon are competitive with those for substrate association/ product dissociation. However, as discussed in later sections, the energies of the... 

Here we describe enzymological properties of representative racemases, epi-merases, and isomerases, and their application to production of various optically active compounds. 

The X-ray crystal structure of P. putida muconate lactonizing enzyme (cycloisomerase) was determined in 1987, and was found to contain an a/(i barrel fold, also found in triosephosphate isomerase and enolase. Remarkably, the structure of P. putida mandelate racemase, which catalyzes a mechanistically distinct reaction earlier in the same pathway, was found in 1990 to have a homologous structure, indicating that the structural fold of the enolase superfamily is able to support a range of enzyme-catalyzed reactions. The P. putida 3-carboxy- r, x-muconate lactonizing enzyme, in contrast, shares sequence similarity with a class II fumarase enzyme, and determination of its structure in 2004 has shown that it shares the same fold as the class II fumarase superfamily, hence these two catalysts of similar reactions have evolved from different ancestors. ... 

Isomerases catalyze molecular isomerizations and include the epimerases, racemases, and intramolecular transferases. An example is shown in Figure 4.8, with the xylose isomerase (EC 5.3.1.5 systematic name, D-xylose ketol-isomerase commonly called glucose isomerase) transformation of a-D-glucopyranose to a-o-fructofuranose. 

A detailed thermod5mamic analysis was performed with lactate dehydrogenase, in the lactate — p5mivate direction, by means of steady-state kinetics and presteady-state kinetic methods, by Laidler and Peterman (1979). A particularly detailed kinetic studies of the energetics of two multistep enzymes, triose-phosphate isomerase and prohne racemase, has been described by the research team of Albery and Knowles (Albery Knowles, 1976, 1986 Knowles, 1991). Apart from these examples, very few complete thermodynamic analyses have been performed with reactions involving more than one substrate or more than one intermediate in reaction. 

EC5. Isomerases these enzymes catalyze changes within one molecule. They include racemases, epimerises, mutases, c/s-tra s-isomerases, etc. Example aldose mutarotase (EC 5.1.3.3)... 

Racemases and cis-trans- so m erases Intramolecular isomerases Intramolecular Intramolecular lyases... 

The recycling of the undesired enantiomer from the enzymatic resolution is of crucial importance particularly on an industrial scale [107]. The classical chemical method consists of the thermal racemization of an amino acid ester at about 150-170°C. Milder conditions can be employed for the racemization of the corresponding amides via intermediate formation of Schiff bases with aromatic aldehydes such as benzaldehyde or salicylaldehyde (Scheme 2.14). More recently, intense research has been devoted to the use of isomerase enzymes (such as amino acid racemases [108]) aiming at the development of dynamic resolution processes. 

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