Aldolases aldolase

Fnictokinase Defidenc)r (Essoitial Fnictosuria) Fructose l-Phoq>hate Aldolase (Aldolase B) Deficiency (Hereditary Iroctose Intolerance)... 

Fructose bisphosphate aldolase— aldolase Hydroxymethylglutaryl-CoA lyase Hydroxymethylglutaryl-CoA synthase Citrate synthase ATP-citrate lyase... 

PHYSICAL ORGANIC CHEMISTRY NOMENCLATURE ALDEHYDE DEHYDROGENASE ALDEHYDE HYDRATION ALDEHYDE OXIDASE ALDEHYDE OXIDOREDUCTASE ALDOSE REDUCTASE Aldehyde reduction to alcohols, BOROHYDRIDE REDUCTION ALDOLASE Aldolase reduction,... 

SORBITOL DEHYDROGENASE FRUCTOSE-1,6-BISPHOSPHATASE FRUCTOSE-2,6-BISPHOSPHATASE D-Fructose 2,6-bisphosphate, 6-PHOSPHOFRUCTO-2-KINASE Fructose-1,6-bisphosphate aldolase, ALDOLASE... 

In brain tissues, specific isoforms of glycolytic enzymes are also expressed there are specific brain isoforms for PFK (PFK-C), fructose-1,6-bisphosphate aldolase (aldolase C), enolase (enolase y), but not for GAPDH. The isoforms bear the same catalytic functions however, they could be specialized to form different ultrastructural entities. For example, muscle PFK (a dissociable tetrameric form) binds to microtubules and bundle them [94, 95], however, the brain isoenzyme (stable tetramer) does not [96]. 

Aldolases - Aldolases catalyze reversible aldol condensations of su-gars. A well-studied enzyme is fructose-1,6-dlphosphate aldolase from rabbit muscle. This enzyme exhibits a high specificity for dihydroxy-acetone phosphate as the nucleophile, but tolerates a range of aldehydes as electrophiles (Scheme II).This broad specificity allows synthesis of sugars such as 6-deoxyfructose and Isotopically labeled glucose... 

An inborn error of liver fractose-1-phosphate aldolase (aldolase B) leads to a condition known as fructose intolerance. The condition is characterized by life-threatening liver damage that can occur after consuming fructose in the diet. Why is it life-threatening ... 

Fructose-b/fphosphate aldolase, aldolase (EC 4.1.2.13) a tetrameric lyase which reversibly cleaves fructose l,6-f>irphosphate into the two triose phosphates, dihydroxyacetone phosphate and o-glyceral-dehyde phosphate. The reaction is analogous to the aldol condensation (CH3CHO + CH3CHO -> CH3-CHOH-CH2-CHO), hence the name of the enzyme. The equilibrium concentrations are 89% fructose huphosphate and 11 % triose phosphate. The enzyme catalyses the condensation of a number of aldehydes with dihydroxyacetone phosphate, and can also cleave fructose 1-phosphate. Liver aldolase (aldolase B, M, 156,000, 4 subunits of A/, 39,000) cleaves fructose l,6-6isphosphate and fructose 1-phosphate at nearly the same rate. Muscle aldolase (aldolase A, M, 1, 000,4 subunits of M 41,000, pi 6.1), however, is more active with the hirphosphate. Aldolase from yeast is inhibited by cysteine, and reactivated by Fe, Zii and Co. Spinach leaf aldolase has a M, of only 120,000 (M, of subunits 30,000). 

Aldolase. Aldolase splits HDP to triose phosphates. These can be identified by their alkali lability, by their conversion to methyl glyoxal in acid, by derivatives of their carbonyl groups, and by enzymatic reactions to be discussed below. The availability of synthetic triose phosphates made individual identification possible, and it was shown that the initial reaction products are equivalent amounts of D-3-phosphoglycer-aldehyde and dihydroxyacetone phosphate, and that these react back to form HDP. The condensation is an example of the well-known aldol condensation, hence the name aldolase (XI). 

Following Its formation D fructose 6 phosphate is converted to its corresponding 1 6 phosphate diester which is then cleaved to two 3 carbon fragments under the mflu ence of the enzyme aldolase... 

This cleavage is a retro aldol reaction It is the reverse of the process by which d fruc tose 1 6 diphosphate would be formed by aldol addition of the enolate of dihydroxy acetone phosphate to d glyceraldehyde 3 phosphate The enzyme aldolase catalyzes both the aldol addition of the two components and m glycolysis the retro aldol cleavage of D fructose 1 6 diphosphate... 

Further steps m glycolysis use the d glyceraldehyde 3 phosphate formed m the aldolase catalyzed cleavage reaction as a substrate Its coproduct dihydroxyacetone phosphate is not wasted however The enzyme triose phosphate isomerase converts dihydroxyacetone phosphate to d glyceraldehyde 3 phosphate which enters the glycol ysis pathway for further transformations... 

TKsubstrate pNZYTffiS IN ORGANIC SYNTHESIS] (Vol 9) D-Glyceraldehyde-3-phosphate[591-57-l]aldolase-cataly zed additions... 

Enzymes, measured in clinical laboratories, for which kits are available include y-glutamyl transferase (GGT), alanine transferase [9000-86-6] (ALT), aldolase, a-amylase [9000-90-2] aspartate aminotransferase [9000-97-9], creatine kinase and its isoenzymes, galactose-l-phosphate uridyl transferase, Hpase, malate dehydrogenase [9001 -64-3], 5 -nucleotidase, phosphohexose isomerase, and pymvate kinase [9001-59-6]. One example is the measurement of aspartate aminotransferase, where the reaction is followed by monitoring the loss of NADH ... 

Aldolases cataly2e the asymmetric condensation of intermediates common in sugar metaboHsm, such as phosphoenolpymvic acid, with suitable aldehyde acceptors. Numerous aldolases derived from plants or animals (Class I aldolases) or from bacteria (Class II) have been examined for appHcations (81). Efforts to extend the appHcations of these en2ymes to the synthesis of unusual sugars have been described (2,81). 

Metabolic Functions. Zinc is essential for the function of many enzymes, either in the active site, ie, as a nondialyzable component, of numerous metahoenzymes or as a dialyzable activator in various other enzyme systems (91,92). WeU-characterized zinc metahoenzymes are the carboxypeptidases A and B, thermolysin, neutral protease, leucine amino peptidase, carbonic anhydrase, alkaline phosphatase, aldolase (yeast), alcohol... 

There are two distinct groups of aldolases. Type I aldolases, found in higher plants and animals, require no metal cofactor and catalyze aldol addition via Schiff base formation between the lysiae S-amino group of the enzyme and a carbonyl group of the substrate. Class II aldolases are found primarily ia microorganisms and utilize a divalent ziac to activate the electrophilic component of the reaction. The most studied aldolases are fmctose-1,6-diphosphate (FDP) enzymes from rabbit muscle, rabbit muscle adolase (RAMA), and a Zn " -containing aldolase from E. coli. In vivo these enzymes catalyze the reversible reaction of D-glyceraldehyde-3-phosphate [591-57-1] (G-3-P) and dihydroxyacetone phosphate [57-04-5] (DHAP). 

Fig. 6. FDP-aldolase-catalyzed addition of electrophiles (94) with DHAP (139—146). Representative R groups ia (94) are given as (a—j) (a) methyl, CH (b)...

KDPG is a member of a yet unexplored group of aldolases that utilize pymvate or phosphoenol pymvate as the nucleophile in the aldol addition. They are quite tolerant of different electrophilic components and accept a large number of uimatural aldehydes (148). The reaction itself, however, is quite specific, generating a new stereogenic center at the C-4 position. 

TV-Acetyl neuraminic acid aldolase [from Clostridium perfringens, TV-acetyIneuraminic acid pyruvate lyase] [9027-60-5] 32,000 [EC 4.1.3.3]. Purified by extraction with H2O,... 

Mavridis, I.M., et al. Structure of 2-keto-3-deoxy-6-phosphogluconate aldolase at 2.8 A resolution. 

Sygusch, J., Beaudry, D., Allaire, M. Molecular architecture of rabbit skeletal muscle aldolase at 2.7 A resolution. Proe. Natl. Aead. Sei. USA 84 ... 

FIGURE 2.15 Influence of the pore size of Sephacryl HR on the separation of proteins of various molecular mass. The protein mixture is composed of ferritin, aldolase, ovalbumin, and chymotrypsinogen A. [Reproduced from Hagel et al. (1989), with permission.]... 

FIGURE 14.2 The breakdown of glucose by glycolysis provides a prime example of a metabolic pathway. Ten enzymes mediate the reactions of glycolysis. Enzyme A, fructose 1,6, hiphos-phate aldolase, catalyzes the C—C bondbreaking reaction in this pathway. 

Wagner, J., Lerner, R. A., and Barbas, C. F., Ill, 1995. Efficient adolase catalytic antibodies that use tlie enamine mechanism of natural enzymes. Science 270 1797-1800. See also tlie discussion entitled Aldolase antibody in Science 270 1737. 

FIGURE 16.8 (a) Phosphoglycolohydroxamate is an analog of the enediolate transition state of the yeast aldolase reaction, (b) Purine riboside, a potent inhibitor of the calf intestinal adenosine deaminase reaction, binds to adenosine deaminase as the 1,6-hydrate. The hydrated form of purine riboside is an analog of the proposed transition state for the reaction. 

Reaction 4 Cleavage of Fructose-1,6-bisP by Fructose Bisphosphate Aldolase... 

Two classes of aldolase enzymes are found in nature. Animal tissues produce a Class I aldolase, characterized by the formation of a covalent Schiff base intermediate between an active-site lysine and the carbonyl group of the substrate. Class I aldolases do not require a divalent metal ion (and thus are not inhibited by EDTA) but are inhibited by sodium borohydride, NaBH4, in the presence of substrate (see A Deeper Look, page 622). Class II aldolases are produced mainly in bacteria and fungi and are not inhibited by borohydride, but do contain an active-site metal (normally zinc, Zn ) and are inhibited by EDTA. Cyanobacteria and some other simple organisms possess both classes of aldolase. 

FIGURE 19.13 (a) A mechanism for the fructose-l,6-bisphosphate aldolase reaction. The Schlff base formed between the substrate carbonyl and an active-site lysine acts as an electron sink, Increasing the acidity of the /3-hydroxyl group and facilitating cleavage as shown. (B) In class II aldolases, an active-site Zn stabilizes the enolate Intermediate, leading to polarization of the substrate carbonyl group. 

The Chemical Evidence for the Schiff Base Intermediate in Class I Aldolases... 

Fructose bisphosphate aldolase of animal muscle is a Class I aldolase, which forms a Schiff base or imme intermediate between the substrate (fructose-1,6-bisP or dihydroxyacetone-P) and a lysine amino group at the enzyme active site. The chemical evidence for this intermediate comes from studies with the aldolase and the reducing agent sodium borohydride, NaBH4. Incubation of fructose bisphosphate aldolase with dihydroxyacetone-P and NaBH4 inactivates the enzyme. Interestingly, no inactivation is observed if NaBH4 is added to the enzyme in the absence of substrate. 

These observations are explained by the mechanism shown in the figure. NaBH4 inactivates Class I aldolases by transfer of a hydride ion (H ) to the imine carbon atom of the enzyme-substrate adduct. The resulting secondary amine is stable to hydrolysis, and the active-site lysine is thus permanently modified and inactivated. NaBH4 inactivates Class I aldolases in the presence of either dihydroxyacetone-P or fructose-1,6-bisP, but inhibition doesn t occur in the presence of glyceraldehyde-3-P. 

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