Sedoheptulose7phosphate

Sedoheptulose-7-phosphate (S7P) is a phosphorylated seven-carbon sugar that functions as an intermediate in central carbon metabolism. It is a key metabolite of the non-oxidative branch of the pentose phosphate pathway (PPP) and also participates in the Calvin cycle of photosynthesis.

In the PPP, S7P is formed by the action of transketolase on xylulose-5-phosphate and ribose-5-phosphate, yielding glyceraldehyde-3-phosphate and sedoheptulose-7-phosphate. It is subsequently involved in a transaldolase reaction with glyceraldehyde-3-phosphate to produce erythrose-4-phosphate and fructose-6-phosphate, thereby linking the PPP with glycolysis and providing precursors for nucleotide biosynthesis and aromatic amino acid synthesis.

In plants and algae, S7P also contributes to the regeneration phase of the Calvin cycle. Through a series of transketolase- and transaldolase-catalyzed steps, carbon skeletons are rearranged to regenerate ribulose-1,5-bisphosphate, enabling continued carbon fixation in chloroplasts.

Chemical and biological context: S7P is one of several sugar phosphates produced and consumed by PPP enzymes. Its presence helps balance carbon flux between ribose-5-phosphate production for nucleotide synthesis and glycolytic intermediates for energy metabolism.

Localization: PPP reactions occur in the cytosol of most organisms; in photosynthetic tissues, related reactions occur in chloroplasts.

Synonyms: sedoheptulose-7-phosphate, S7P.