Glyceraldehyde-3-phosphate synthesis

Chloroplast glyceraldehyde Phosphate dehydrogenase Catalyzes reactions in the Calvin cycle, glucose synthesis... 

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

They accomplish the reduction of 3-phosphoglycerate, the primary product of COg fixation, to glyceraldehyde-3-phosphate so that carbohydrate synthesis becomes feasible. 

When carbon rearrangements are balanced to account for net hexose synthesis, five of the glyceraldehyde-3-phosphate molecules are converted to dihy-droxyacetone phosphate (DHAP). Three of these DHAPs then condense with three glyceraldehyde-3-P via the aldolase reaction to yield 3 hexoses in the form... 

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]. 

Clavulanic acid is synthesized by the condensation of L-arginine and D-glyceraldehyde-3-phosphate (G3P) as the first step [75,77] (Figure 12.2). A series of experiments revealed that the synthesis of clavulanic acid was limited by the availability of the C3 precursor, resulting from the species s limited ability to assimilate glucose [78]. Thus, the enhancement of clavulanic acid production requires alleviation of competition from other pathways for a C3 precursor [79]. 

A practical, inexpensive one-step procedure was developed for the RhaD-catalyzed gram-scale synthesis of L-fructose. The requirement for DHAP as the donor substrate was circumvented by use of borate buffer, presumably by in situ formation of borate esters as a phosphate ester mimic. Racemic glyceraldehyde was also used, as the enzyme preferentially accepted the L-enantiomer as a substrate. The method can also be apphed to other products, including L-rhamnulose, and towards a two-step synthesis of L-iminocychtols. ... 

Aldolase catalyses both aldol and reverse aldol reactions according to an organism s needs. In glycolysis, the substrate fmctose 1,6-diphosphate is cleaved by a reverse aldol reaction to provide one molecule of glyceraldehyde 3-phosphate and one molecule of dihydroxyacetone phosphate. In carbohydrate synthesis, these two compounds can be coupled in an aldol reaction to produce fmctose 1,6-diphosphate. 

The formation of 1,3-bisphosphoglycerate involves the synthesis of a high-energy phosphate bond as the aldehyde of glyceraldehyde 3-phosphate is oxidized to a carboxylic acid and then phosphorylated by reaction with inorganic phosphate. 

The formation of ATP (or GTP) at the expense of the energy released by the oxidative decarboxylation of a-ketoglutarate is a substrate-level phosphorylation, like the synthesis of ATP in the glycolytic reactions catalyzed by glyceraldehyde 3-phosphate dehydrogenase and pyruvate kinase (see Fig. 14-2). The GTP formed by succinyl-CoA synthetase can donate its terminal phosphoryl group to ADP to form ATP, in a reversible reaction catalyzed by nucleoside diphosphate kinase (p. 505) ... 

FIGURE 20-4 The three stages of C02 assimilation in photosynthetic organisms. Stoichiometries of three key intermediates (numbers in parentheses) reveal the fate of carbon atoms entering and leaving the cycle. As shown here, three C02 are fixed for the net synthesis of one molecule of glyceraldehyde 3-phosphate. This cycle is the photosynthetic carbon reduction cycle, or the Calvin cycle. 

The chloroplast stroma contains all the enzymes necessary to convert the triose phosphates produced by C02 assimilation (glyceraldehyde 3-phosphate and dihydroxyacetone phosphate) to starch, which is temporarily stored in the chloroplast as insoluble granules. Aldolase condenses the trioses to fructose 1,6-bisphos-phate fructose 1,6-bisphosphatase produces fructose 6-phosphate phosphohexose isomerase yields glucose 6-phosphate and phosphoglucomutase produces glucose 1-phosphate, the starting material for starch synthesis (see Section 20.3). 

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