title: The significance of sedoheptulose 1,7-bisphosphate in the metabolism and regulation of the pentose pathway in liver.
abstract: Rat liver cytosolic enzyme preparation catalyses the formation of sedoheptulose 1,7-P2 (60% of total heptulose-P formed) from hexose 6-P and triose 3-P (reverse mode of pentose pathway operation). Smaller amounts of sedoheptulose 1,7-P2 are also formed from ribose 5-P during the non-oxidative synthesis of hexose 6-P (forward pentose pathway operation). The apparent absence of erythrose 4-P in biological systems may be explained by its contribution to carbons 4,5,6 and 7 of sedoheptulose 1,7-P2 as well as its pronounced ability to exist in dimeric form. Apart from the aldolase catalyzed formation of sedoheptulose 1,7-P2, 6-phosphofructokinase also catalyses its formation from sedoheptulose 7-P and fructose 1,6-bisphosphatase catalyses its dephosphorylation. These three enzymes may contribute to the regulation of carbon flux through the near equilibrium reactions of the non-oxidative pentose phosphate pathway in vivo. The phosphotransferase enzyme of the L-type pentose pathway is also able to catalyse the interconversion of sedoheptulose mono and bisphosphates via D-glycero D-ido octulose-P.
mesh_terms: D000818:Animals; D050260:Carbohydrate Metabolism; D002852:Chromatography, Ion Exchange; D003600:Cytosol / Q000201:enzymology; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D010427:Pentose Phosphate Pathway / Q000187:drug effects*; D010766:Phosphorylation; D051381:Rats; D013403:Sugar Phosphates / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D013403:Sugar Phosphates; C022079:sedoheptulose 1,7-bisphosphate