title: Glucose 6-phosphate formation by L-type pentose phosphate pathway reactions of rat liver in vitro: further evidence.
abstract: An investigation of the mechanism in vitro of the non-oxidative segment of the pentose phosphate pathway using [5-14C]ribose 5-phosphate as a prediction labelling substrate with rat liver enzyme preparation is reported. Glucose 6-phosphate formed during the initial 0.5 h of reaction was heavily labelled in C-1 and thus is consistent with the prediction of the liver (L)-type pentose phosphate pathway (theoretically C-1/C-6 = 0.5). The reaction sequences of the fat (F-) type pentose phosphate pathway exclusively confine 14C to C-6 of glucose 6-phosphate. The presence of L-type reactions was further affirmed by the formation of D-arabinose 5-phosphate and D-glycero-D-ido-octulose phosphate which were identified and measured during the initial 2 h of incubation using gas liquid chromatography. After 3 h the concentration of 14C in C-1 of glucose 6-phosphate gradually declined and by 17 h of incubation the ratio of 14C in C-1/C-6 was 0.1. Possible reasons for the late changes in 14C-isotope distributions towards a pattern consistent with a contribution of F-type pentose phosphate pathway are given.
mesh_terms: D000818:Animals; D002849:Chromatography, Gas; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000096:biosynthesis*; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D010427:Pentose Phosphate Pathway; D051381:Rats; D012267:Ribosemonophosphates / Q000378:metabolism; D013237:Stereoisomerism; D013997:Time Factors
chemical_list: D005958:Glucosephosphates; D012267:Ribosemonophosphates; C031626:ribose-5-phosphate; D019298:Glucose-6-Phosphate