D-fructose 1,6-bisphosphate

The D-fructose 1,6-bisphosphate aldolase (FruA EC 4.1.2.13) catalyzes in vivo the equilibrium addition of (25) to D-glyceraldehyde 3-phosphate (GA3P, (18)) to give D-fructose 1,6-bisphosphate (26) (Figure 10.14). The equilibrium constant for this reaction of 10 strongly favors synthesis [34]. The enzyme occurs ubiquitously and has been isolated from various prokaryotic and eukaryotic sources, both as class I and class II forms [30]. Typically, class I FruA enzymes are tetrameric, while the class II FruA are dimers. As a rule, the microbial class II aldolases are much more stable in solution (half-lives of several weeks to months) than their mammalian counterparts of class I (few days) [84-86]. 

This hydrolase [EC 3.1.3.11] catalyzes conversion of d-fructose 1,6-bisphosphate to D-fructose 6-phosphate and orthophosphate. 

This enzyme [EC 2.7.1.11], also known as phosphohexo-kinase and phosphofructokinase 1, catalyzes the reaction of ATP with D-fructose 6-phosphate to produce ADP and D-fructose 1,6-bisphosphate. Both D-tagatose 6-phosphate and sedoheptulose 7-phosphate can act as the sugar substrate. UTP, CTP, GTP, and ITP all can act as the nucleotide substrate. This enzyme is distinct from that of 6-phosphofructo-2-kinase. See also ATP GTP Depletion... 

D-fructose 1,6-bisphosphate 2 (FruA E.C. 4.1.2.13), D-tagatose 1,6-bisphosphate 4 (TagA E.C. 4.1.2.40), L-fuculose 1-phosphate 5 (FucA, E.C. 4.1.2.17), and L-rhamnulose 1-phosphate 4 (RhuA, E.C. 4.1.2.19). From previous studies, we have DHAP aldolases with all four possible specificities readily available, we have demonstrated their broad substrate tolerance for variously substituted aldehydes, and we have investigated their stereoselectivity profile with non-natural substrates [3-6]. 

Based on the stereospecific transketolase-catalyzed ketol transfer from hydroxy-pyruvate (20) to D-glyceraldehyde 3-phosphate (18), we have thus developed a practical and efficient one-pot procedure for the preparation of the valuable keto-sugar 19 on a gram scale in 82% overall yield [29]. Retro-aldolization of D-fructose 1,6-bisphosphate (2) in the presence of FruA with enzymatic equilibration of the C3 fragments is used as a convenient in-situ source of the triose phosphate 18 (Scheme 2.2.5.8). Spontaneous release of CO2 from the ketol donor 20 renders the overall synthetic reaction irreversible [29]. 

Scheme 2.2.5.S Multi-enzymatic route for the stereoselective synthesis of D-xylulose 5-phosphate 19 from commercial D-fructose 1,6-bisphosphate (abbreviations TPI, triose phosphate isomerase TK, transketolase).

While the lyases that transfer a pyruvate unit form only a single stereogenic center, the group of dihydroxyacetone-phosphate-(DHAP, 41)-dependent aldolases create two new asymmetric centers, one each at the termini of the new C-C bond. A particular advantage for synthetic endeavors is the fact that Nature has evolved a full set of four stereochemically-complementary aldolases [189] (Scheme 6) for the retro-aldol cleavage of diastereoisomeric ketose 1-phosphates— D-fructose 1,6-bisphosphate (42 FruA), D-tagatose 1,6-bisphosphate (43 TagA), L-fuculose 1-phosphate (44 FucA), and L-rhamnulose 1-phosphate (45) aldolase (RhuA). In the direction of synthesis this formally allows the... 

In vivo, the D-fructose 1,6-bisphosphate aldolase (FruA EC 4.1.2.13) catalyzes the pivotal reaction of the glycolysis pathway the equilibrium addition of 41 to D-glyceraldehyde 3-phosphate (GA3P, 12) to give D-fructose 1,6-bisphosphate (42) [43]. The equilibrium constant of 104 M 1 strongly favors synthesis [229]. 

Reactions with 1,3-dihydroxyace tone phosphate None added D-fructose 1,6-bisphosphate 40 80 A" 1.7 TPF 3 31... 

Reactions with D-fructose 1,6-bisphosphate Propanal 5,6-dideoxy-D-fAreo-hexulose 1-phosphate 1100 73 Ac 1.4 TW1 1.8 32... 

Step 3 is the phosphorylation of a-D-fructose 6-phosphate to a-D-fructose 1,6-bisphosphate. The enzyme is phosphofructokinase and ATP and Mg2+ are required. 

The mechanism of Step 4 involves a retro-aldol condensation reaction on the open-chain form of D-fructose 1,6-bisphosphate. This reaction, and the origin of the carbon atoms in the products, is shown below. 

Fig. 8.4 The glycolysis pathway in Saccharo-myces and the biosynthesis of ethanol and glycerol. Compounds DHAP, dihydroxyl-acetone monophosphate Fru6P, D-fructose-6-phosphate Frul,6P2, D-fructose-1,6-bisphosphate GA3P, D-glyceraldehyde-3-phosphate GL3P, sn-glycerol-3-phosphate GLAP2, phosphoglycerate-3-phosphate ...

N. Blom, J. Sygusch, Product binding and role of the C-termlnal region in class I D-fructose 1,6-bisphosphate aldolase, Nat. Struct. Biol. 4 (1997), 36-39... 

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