title: The measurement of xylulose 5-phosphate, ribulose 5-phosphate, and combined sedoheptulose 7-phosphate and ribose 5-phosphate in liver tissue.
abstract: A modification of the method of Kauffman et al. (F. C. Kauffman, J. G. Brown, J. V. Passonneau, and O. H. Lowry (1969) J. Biol. Chem. 244, 3647-3653) for the spectrophotometric determination of xylulose 5-phosphate, ribulose 5-phosphate, and combined ribose 5-phosphate and sedoheptulose 7-phosphate in tissue extract is presented. Using commercially available enzymes all three assays come to a clear endpoint with the assays described. Values for these metabolites in liver in three dietary states are reported; 48 h starved, ad libitum feeding of standard NIH rat ration, and meal feeding of a fat-free diet. Xylulose 5-phosphate values were 3.8 +/- 0.3, 8.6 +/- 0.3, and 66.3 +/- 8.3 nmol/g. Ribulose 5-phosphate values were 3.4 +/- 0.3, 5.8 +/- 0.2, and 37.1 +/- 5.3 nmol/g. Combined ribose 5-phosphate and sedoheptulose 7-phosphate were 29.3 +/- 0.3, 38.2 +/- 1.2, and 108.2 +/- 14.5 nmol/g. The ratio of measured tissue content of [xylulose 5-phosphate]/[ribulose 5-phosphate] was found to be 1.12 +/- 0.07 in starved animals, 1.48 +/- 0.04 in ad libitum fed animals and 1.78 +/- 0.03 in low-fat meal fed animals. These data are in good agreement with the range of equilibrium constants reported for this reaction, suggesting that the ribulose 5-phosphate 3-epimerase reaction (EC 5.1.3.1) is a near equilibrium reaction despite a more than 10-fold change in the tissue content of these metabolites.
mesh_terms: D000818:Animals; D004032:Diet; D008099:Liver / Q000032:analysis*; D008297:Male; D010427:Pentose Phosphate Pathway; D010428:Pentosephosphates / Q000032:analysis*; D051381:Rats; D011919:Rats, Inbred Strains; D012267:Ribosemonophosphates / Q000032:analysis; D012274:Ribulosephosphates / Q000032:analysis; D013217:Starvation / Q000378:metabolism; D013403:Sugar Phosphates / Q000032:analysis
chemical_list: D010428:Pentosephosphates; D012267:Ribosemonophosphates; D012274:Ribulosephosphates; D013403:Sugar Phosphates; C020495:sedoheptulose 7-phosphate; C031524:ribulose 5-phosphate; C031626:ribose-5-phosphate; C031625:xylulose-5-phosphate