Isomerases epimerases

Isomerase Glucose isomerases, epimerases, mutases, lyases, topoisomerases... 

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

Ribulose 5-phosphate is capable of a reversible isomerization to other pentose phosphates-xylulose 5-phosphate and ribose 5-phosphate. These reactions are catalyzed by two respective enzymes, viz., pentose-phosphate epimerase and pentose-phosphate isomerase, according to the scheme below ... 

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 ... 

The isomerases comprise enzyme class 5 and they are enzymes catalyzing changes within one molecule. Important subclasses are racemaces and epimerases (EC 5.1) and intramolecular oxidoreductases (EC 5.3). 

Subsequent Reactions Catalyzing 6-Deoxyhexose Formation 3,5-Epimerase and Reductase. After the formation of the 4-keto intermediate, a step common to all deoxyhexose formations, at least two and possibly three additional enzymes are necessary for the biosynthesis of the end product. This sequence of transformations is illustrated in Figure 3. The first step is the conversion of the 4-keto-6-deoxy-hexose intermediate described above. The intermediates in brackets are postulated and are assumed to be bound to the enzyme. An enzyme (or enzymes), referred to below as 3,5-isomerase, catalyzes epimerizations at carbons 3 and 5, probably via the enediol form. The epimerizations are followed by a... 

Ribulose 5-phosphate 3-epimerase UDP-glucose 4-epimerase D-Glyceraldehyde 3-phosphate ketol isomerase... 

Ribulose-5-phosphate (3.13) can be converted to ribose-5-phosphate (3.14) and xylulose 5-phosphate (3.15), by the enzymes ribose-5-phosphate isomerase and ribulose 5-phosphate 3-epimerase, respectively. The two pentose-phosphate molecules, 3.14 and 3.15, are converted to a C3 and a C7 sugar-phosphate, glyceraldehyde 3-phosphate (3.4) and sedoheptulose-7-phosphate (3.16), respectively, via the action of atransketolase. 

PFACRI N -[(5 -phosphoribosyl)formimino]-5-aminoimidazole-4-carboxamide ribonucleotide isomerase ImGPS imidazole 3-glycerol phosphate synthase OMPDC orotidine 5 -phosphate decarboxylase R5PE ribulose 5-phosphate epimerase HUMPS hex-3-ulose monophosphate... 

Monocupins include bacterial carbohydrate isomerases and epimerases as well as germins and germin-like proteins (GLPs). So far, Cit s 1 from orange is one of the few members of the germin family, which has been reported to act as an allergen. 

The 5-carbon sugar phosphates are interconverted by the action of epimerase and isomerase to yield ribulose-5-phosphate, which is phosphorylated by the enzyme ribulose phosphate kinase to make RuBP, the acceptor of C02. 

L-arabinose isomerase, which interconverts L-arabinose and L-ribulose araB, L-ribulokinase, which uses ATP to phosphorylate L-ribulose at C-5 araD, L-ribulose 5-phosphate epimerase, which interconverts L-ribulose 5-phosphate and L-xylulose 5-phosphate talB, transaldolase and tktA, transketolase. 

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

Figure 6.4. Role of transketolase in the pentose phosphate pathway. Glucose 6-phosphate dehydrogenase, EC 1.1.1.49 phosphogluconate dehydrogenase, EC 1.1.1.44 rihulose-phosphate epimerase, EC 5.1.3.1 phosphorihose isomerase, EC 5.3.1,6 transketolase, EC 2.2.1.1 and transaldolase, EC 2.2.I.2.

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