DHAP from dihydroxyacetone

Reduction of dihydroxyacetone phosphate (DHAP) from glycolysis by glycerol 3-P dehydrogenase, an enzyme in both adipose tissue and liver... 

Scheme 4.4 Chemical routes to DHAP. (a) Routes from dihydroxyacetone dimer. The stable precursors are converted to DHAP by acid hydrolysis, (b) Route from 1,3-dibromoacetone. The stable precursor is converted to DHAP by treatment with NaOH.

D) the glycerol moiety may be derived from dihydroxyacetone phosphate (DHAP) but not from blood glycerol... 

Figure 26.1 PATHWAY INTEGRATION Sources of intermediates in the synthesis of triacylglycerols and phospholipids. Phosphatidate, synthesized from dihydroxyacetone phosphate (DHAP) produced In glycolysis and fatty acids, can be further processed to produce triacylglycerol or phospholipids. Phospholipids and other membrane lipids are continuously produced in all cells.

The aldol reaction is extensively used in Nature as in the laboratory to make C-C bonds and some aldolases have been used in asymmetric synthesis. One of the most popular has been the fructose-6-phosphate aldolase44 from rabbit muscle, familiarly known as RAMA. The enzymatic reaction combines the enol from dihydroxyacetone phosphate (DHAP) 142 with glyceraldehyde-3-phosphate 143 in a diastereo- and enantioselective aldol reaction. PO in these diagrams means phosphate. 

Fig. 4. Ether phospholipid synthesis from dihydroxyacetone-phosphate. (A) Dihydroxyacetone-P acyl transferase (DHAPAT). The first step of ether phospholipid synthesis is catalyzed by peroxisomal DHAPAT. This enzyme is a required component of complex ether lipid biosynthesis and its role cannot be assumed by a cytosolic enzyme that also forms acyldihydroxyacetone-P. (B) Ether bond formation by alkyl-DHAP synthase. The reaction that forms the 0-alkyl bond is catalyzed by alkyl-DHAP synthase and is thought to proceed via a ping-pong mechanism. Upon binding of acyl-DHAP to the enzyme alkyl-DHAP synthase, the pro-f hydrogen at carbon atom 1 is exchanged by enolization of the ketone, followed by release of the acyl moiety to form an activated enzyme-DHAP complex. The carbon atom at the 1-position of DHAP in the enzyme complex is thought to carry a positive charge that may be stabilized by an essential sulfhydryl group of the enzyme thus, the incoming alkox-ide ion reacts with carbon atom 1 to form the ether bond of alkyl-DHAP. It has been proposed that a nucleophilic cofactor at the active site covalently binds the DHAP portion of the substrate.

Figure 19.2 schematically depicts the primary pathways of prokaryotic and eukaryotic glycerophospholipid biosynthesis. Note that the center pathway shown in purple occurs in both prokaryotic and eukaryotic cells. Phosphatidic acid, the branch point between the synthesis of fats and other glycerophospholipids, can be made via three different pathways in eukaryotes-from glycerol-3-phosphate (Figure 19.3), from diacylglycerol (Figure 19.2), and from dihydroxyacetone phosphate (DHAP) (see here). 

The cytoplasmic pool of plastidially derived acyl-CoAs can in turn serve as substrates for the reactions of TAG assembly, which occur through the catalytic action of membrane-bound enzymes in the ER in a process that involves membrane metabolism (Weselake 2005). The glycerol backbone used for TAG bioassembly is derived from OT-glycerol-S-phosphate (G3P), which is produced from dihydroxyacetone phosphate (DHAP) and reduced nicotinamide adenine dinucleotide (NADH)... 

Since many of the aldolases use DHAP as the nucleophilic component of the reaction, attention has been given to devising efficient methods for its preparation starting from dihydroxyacetone. The synthesis of DHAP can be achieved in high overall yield according to the procedure shown... 

Chain-extended Compounds. - Unusual hexoses and higher carbon sugars have been produced by use of fructose 1,6-diphosphate aldolase which catalysed firstly, in combination with triosephosphate isomerase, the release of dihydroxyacetone phosphate (DHAP) from fructose 1,6-diphosphate and secondly the stereospecific condensation of DHAP with a variety of simple aldehydes. Two examples are given in Scheme 7. ... 

Apparently, all DHAP aldolases are highly specific for the donor component 22 for mechanistic reasons [29]. For synthetic applications, two equivalents of 22 are conveniently generated in situ from commercial fructose 1,6-bisphosphate 23 by the combined action of FruA and triose phosphate isomerase (EC 5.3.1.1) [93,101]. The reverse, synthetic reaction can be utilized to prepare ketose bisphosphates, as has been demonstrated by an expeditious multienzymatic synthesis of the (3S,4S) all-cis-configurated D-tagatose 1,6-bisphosphate 24 (Fig. 13) from dihydroxyacetone 27, including a cofactor-dependent phosphorylation, by employing the purified TagA from E. coli (Fig. 13) [95,96]. 

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). 

The chemical reaction catalyzed by triosephosphate isomerase (TIM) was the first application of the QM-MM method in CHARMM to the smdy of enzyme catalysis [26]. The study calculated an energy pathway for the reaction in the enzyme and decomposed the energetics into specific contributions from each of the residues of the enzyme. TIM catalyzes the interconversion of dihydroxyacetone phosphate (DHAP) and D-glyceraldehyde 3-phosphate (GAP) as part of the glycolytic pathway. Extensive experimental studies have been performed on TIM, and it has been proposed that Glu-165 acts as a base for deprotonation of DHAP and that His-95 acts as an acid to protonate the carbonyl oxygen of DHAP, forming an enediolate (see Fig. 3) [58]. 

A mixture of dihydroxyacetone and inorganic arsenate can replace DHAP due to the transient formation of a monoarsenate ester which is recognized by the aldolase as a DHAP mimic21. This approach suffers from the high toxicity of arsenate, especially at the relatively high levels (>0.5 M) needed for efficient conversion, and from problems in product isolation. 

Functionally related to FruA is the novel class I fructose 6-phosphate aldolase (FSA) from E. coli, which catalyzes the reversible cleavage of fructose 6-phosphate (30) to give dihydroxyacetone (31) and d-(18) [90]. It is the only known enzyme that does not require the expensive phosphorylated nucleophile DHAP for synthetic purpose. 

The main group of aldolases from the biocatalytic point of view is, arguably, the one that uses dihydroxyacetone phosphate (DHAP) as donor. Here, we will concentrate on that appHcations in which DHAP-dependent aldolase are part of a multi-enzyme system or, alternatively, on those in which the aldolase-catalyzed reaction is key in a multi-step synthetic pathway. 

FIGURE 21-21 Glyceroneogenesis. The pathway is essentially an abbreviated version of gluconeogenesis, from pyruvate to dihydroxyacetone phosphate (DHAP), followed by conversion of DHAP to glycerol 3-phosphate, which is used for the synthesis of triacylglycerol. 

The probable reaction mechanism of triosephosphate isomerase. The y-carboxylate group of Glu 165 acts as a general base to remove a proton from C-l of the substrate, dihydroxyacetone phosphate (DHAP). This generates a planar ene-diolate intermediate that has two... 

The metabolic pool that consists of fructose-1,6-bisphosphate and the two triose phosphates—glyceralde-hyde-3-phosphate and dihydroxyacetone phosphate (DHAP)—is somewhat different from the other two pools of intermediates in glycolysis because of the nature of the chemical relationships between these compounds. In the other pools the relative concentrations of the component compounds at equilibrium are independent of the absolute concentrations. Because of the cleavage of one substrate into two products, the relative concentrations of fructose-1,6-bisphosphate and the triose phosphates are functions of the actual concentrations. For such reactions, the relative concentrations of the split products must increase with dilution. (For the reaction A v B + C, the equilibrium constant is equal to [B][C]/[A], If the concentration of A decreases, for example, by a factor of 4, equilibrium is... 

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