Glycolysis aldol reactions

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... 

Problem 29.8 Look at the entire glycolysis pathway and make a list of the kinds of organic reactions that take place—nucleophilic acyl substitutions, aldol reactions, ElcB reactions, and so forth. 

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. 

This is a reverse aldol reaction, similar to step 4 of glycolysis. 

As was true in step 4 of glycolysis (Figure 29.4), this aldol reaction actually takes place not on the free ketone but on an imine (Schiff base) formed by reaction of dihydroxyacetone phosphate with a side-chain -NH2 group on the enzyme. Loss of a proton from the neighboring carbon then generates an enamine (Section 19.9), an aldol-like reaction ensues, and the product is hydrolyzed. 

M CHEMISTRY OF Retro-Aldol Reaction in Glycolysis—Dividing Assets V to Double the ATP Yield... 

Glycolysis involves many steps and is accompanied by the conversion of two molecules of ADP into ATP. This metabolic process therefore generates the necessary ATP for muscle contraction. One of the steps involved in glycolysis is a retro-aldol reaction, which is achieved with the help of an enzyme called aldolase. 

In an early step of glycolysis, the energy-producing part of glucose metabolism, the enzyme aldolase catalyzes a reverse or retro-aldol reaction. 

See "The Chemistry of... A Retro-Aldol Reaction in Glycolysis Dividing Assets to Double the ATP Yield" for an important biochemical application that increases the energy yield from glucose. 

Step of Figure 29.13 Aldol Reaction Dihydroxyacetone phosphate and glyceraldehyde 3-phosphate, the two 3-carbon units produced in step 7, join by an aldol reaction to give fmctose 1,6-bisphosphate, the reverse of step 4 in glycolysis (Figure 29.9 on page 1178). As in glycolysis, the reaction is catalyzed in plants and animals by a class 1 aldolase and takes place on an iminium ion formed by reaction of dihydroxyacetone phosphate with a side-chain... 

N-proteded ester 611 -Schiff bases 367,369 glycolate aldol reaction 164 glycolysis 795... 

Fructose-6-phosphate formed from the isomerization discussed above is further phos-phorylated during glycolysis to fructose-1,6-diphosphate (108), which is then cleaved by fructose-1,6-bisphosphate aldolase to afford dihydroxy acetone phosphate (109) and glyceraldehyde-3-phosphate (110). This cleavage reaction is the reverse of an aldol condensation discussed in Section II.C and during gluconeogenesis. In the latter case, fructose-1,6-bisphosphate aldolase catalyzes the reverse reaction herein via aldol condensation of the ketose 109 and the aldose 110 to form linear fructose-1,6-bisphosphate (108) . 

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