ribulos5fosfat

Ribulose-5-phosphate (often abbreviated Ru5P; Swedish: ribulos-5-fosfat) is a phosphorylated ketopentose that functions as a key intermediate in cellular carbohydrate metabolism. It is produced in the oxidative phase of the pentose phosphate pathway by decarboxylation of 6-phosphogluconate and can be converted enzymatically into other five-carbon sugars.

Enzymes acting on ribulose-5-phosphate include phosphopentose isomerase, which converts it to ribose-5-phosphate for nucleotide and nucleic acid synthesis, and ribulose-phosphate 3-epimerase, which interconverts it with xylulose-5-phosphate. In photosynthetic organisms, ribulose-5-phosphate is a precursor of ribulose-1,5-bisphosphate (RuBP) via the enzyme phosphoribulokinase; RuBP is the CO2 acceptor in the Calvin–Benson cycle.

Ribulose-5-phosphate participates in redox balance and biosynthetic flux by linking the pentose phosphate pathway to glycolysis and nucleotide biosynthesis. Its concentrations and flux are regulated by the activity of upstream dehydrogenases in the pentose phosphate pathway and by the demand for ribose phosphates and reducing power (NADPH). The compound is found in the cytosol of many organisms and in the plastids of plants and algae where photosynthetic carbon fixation occurs.