Origins of the hydrogen bound to carbon 1 of glucose in fasting: significance in gluconeogenesis quantitation

Origins of the hydrogen bound to carbon 1 of glucose in fasting: significance in gluconeogenesis quantitation. Healthy subjects ingested (H2O)-H-2. H-2 enriched the hydrogen bound to carbon 1 of blood glucose 1.3 to 1.8 times more than the hydrogens bound to carbon 6. Enrichment at carbon 1 was more than at carbon 5 after 14 h, but not after 42 h, of fasting. After overnight fasting, when [2,3-H-3]succinate was infused, 34 times as much H-3 was bound to carbon 6 as to carbon 1. On [1-H-2,1-H-3,1-C-14] galactose infusion, the ratios of H-2 to C-14 and of H-3 to C-14 in blood glucose were 30% less than in the galactose. H-3 at carbon 6 was 1% of that at carbon 1 of the glucose. Thus, although the two hydrogens bound to carbon 1 and the two bound to carbon 6 of fructose 6-phosphate (P) during gluconeogenesis are equally enriched in H-2 via pyruvate's equilibration with alanine, one of each is further enriched via hydration of fumarate that is converted to glucose. That hydrogen at carbon 1 of fructose 6-phosphate (p) is also enriched in fructose 6-P's equilibration with mannose 6-P. H-2 from (H2O)-H-2 at carbon 1 to carbon 2 of blood glucose cannot then quantitate gluconeogenesis because of [1-H-2]glucose formation during glycogenolysis. Triose-P cycling has a minimal effect on quantitation. H-2 recovery in glucose from [1-H-2]galactose does not quantitate galactose conversion via UDP-glucose to glycogen.