Solved: One of the steps in the pentose phosphate pathway for glucose catabolism is the

Chapter 29, Problem 29.48

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One of the steps in the pentose phosphate pathway for glucose catabolism is the reaction of sedoheptulose 7-phosphate with glyceraldehyde 3-phosphate in the presence of a transaldolase to yield erythrose 4-phosphate and fructose 6-phosphate. Glyceraldehyde 3-phosphate Erythrose 4-phosphate H OH H OH CH2OPO3 2 O H C Sedoheptulose 7-phosphate H OH CH2OPO3 2 H OH H OH HO H CH2OPO3 2 H OH O H C C O CH2OH Fructose 6-phosphate H OH H OH CH2OPO3 2 HO H C O CH2OH (a) The first part of the reaction is formation of a protonated Schiff baseof sedoheptulose 7-phosphate with a lysine residue in the enzymefollowed by a retro-aldol cleavage to give an enamine plus erythrose4-phosphate. Show the structure of the enamine and the mechanism bywhich it is formed.(b) The second part of the reaction is nucleophilic addition of the enamineto glyceraldehyde 3-phosphate followed by hydrolysis of the Schiff baseto give fructose 6-phosphate. Show the mechanism.