P

Stage 2: Conversion of 3-Phosphoglycerate to Glyceraldehyde 3-Phosphate The 3-phosphoglycerate formed in stage 1 is converted to glyceraldehyde 3-phosphate in two steps that are essentially the reversal of the corresponding steps in glycolysis, with one exception: the nucleotide cofactor for the reduction of 1,3-bisphosphoglycerate is NADPH rather than NADH (Fig. 20-9). The chloroplast stroma contains all the glycolytic enzymes except phos-phoglycerate mutase. The stromal and cytosolic enzymes are isozymes; both sets of enzymes catalyze the same reactions, but they are the products of different genes.

In the first step of stage 2, the stromal 3-phospho-glycerate kinase catalyzes the transfer of a phospho-ryl group from ATP to 3-phosphoglycerate, yielding 1,3-bisphosphoglycerate. Next, NADPH donates electrons in a reduction catalyzed by the chloroplast-specific isozyme of glyceraldehyde 3-phosphate dehydroge-nase, producing glyceraldehyde 3-phosphate and Pi. Triose phosphate isomerase then interconverts glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.

Fructose 6-phosphate

Pj-triose phosphate antiporter

Glyceraldehyde 3-phosphate

Fructose 6-phosphate

Pj-triose phosphate antiporter

Glyceraldehyde 3-phosphate glycolysis

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