title: Mechanism and quantitative contribution of the pentose pathway to the glucose metabolism of Morris hepatoma 5123C.
abstract: An investigation of the mechanism and quantitative contribution of the pentose phosphate pathway in the glucose metabolism of Morris Hepatoma 5123C is reported. Morris Hepatoma 5123C has an active non-oxidative segment of pentose pathway as judged by its ability to convert ribose 5-P to hexose 6-P in a standard assay. Based on compliance with qualitative and quantitative criteria, the cells exhibit the L-type pentose pathway reaction sequence rather than the F-type pathway. This compliance included the formation of intermediates characteristic of the L-type pathway, namely arabinose 5-P, octulose mono- and bisphosphates and sedoheptulose 1,7-bisphosphate, during the dissimilation of ribose 5-P to hexose 6-P. The intermediary role of arabinose 5-P was suggested by the incorporation of its carbon into various intermediates and products of the pentose pathway. Intermediary roles for ido octulose mono- and bisphosphates were supported by their participation in the reaction catalyzed by the phosphotransferase enzyme of the L-type pentose pathway. Presence of L-type PP reactions was further affirmed by 14C-prediction labelling experiments using [5-14C]- and [2-14C]glucose as specifically labelled substrates. Using two methods of measurement, the F-type pentose cycle made a negligibly small contribution to glucose metabolism, while the measured value of the L-type pentose pathway accounted for 30% (approx.) of the total glucose metabolism of these cells, a value consistent with the high activity of the enzymes of the L-type pentose pathway in Morris Hepatoma 5123C cells and the very high activity of the non-oxidative segment of the pathway in vitro. The findings validate the proposal that the L-type pentose pathway reactions constitute the non-oxidative segment of the pathway in Morris Hepatoma 5123C cells. Reasons involving pyruvate recycling reactions show why there is low incorporation of 14C-isotope in C-1 of glucose 6-P, when [4,5,6-14C]glucose and [6-14C]glucose are L-type PP test substrates in intact cells.
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation; D005947:Glucose / Q000378:metabolism*; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism; D006600:Hexosephosphates / Q000378:metabolism; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D008297:Male; D010084:Oxidation-Reduction; D010427:Pentose Phosphate Pathway; D010428:Pentosephosphates / Q000378:metabolism; D010429:Pentoses / Q000378:metabolism; D051381:Rats; D012267:Ribosemonophosphates / Q000378:metabolism
chemical_list: D005958:Glucosephosphates; D006600:Hexosephosphates; D010428:Pentosephosphates; D010429:Pentoses; D012267:Ribosemonophosphates; C028055:arabinose 5-phosphate; C031626:ribose-5-phosphate; D019298:Glucose-6-Phosphate; D005947:Glucose