Open Access13 C NMR studies of gluconeogenesis in rat liver cells: Utilization of labeled glycerol by cells from euthyroid and hyperthyroid rats
Author(s) -
S. M. Cohen,
Satoshi Ogawa,
R. G. Shulman
Publication year - 1979
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.76.4.1603
Subject(s) - gluconeogenesis , euthyroid , glycerol , chemistry , biochemistry , endocrinology , medicine , metabolism , biology , hormone
The gluconeogenic pathway from [2-13 C]glycerol and [1,3-13 C]glycerol has been followed in suspensions of isolated rat hepatocytes at 25°C by13 C NMR at 90.5 MHz. The flow of label through the major pathway from glycerol to L-glycerol 3-phosphate and into glucose was followed in cells from control and triiodothyronine-treated rats. Treatment increased the rates of glucose formation and glycerol consumption 2-fold and decreased the αGP level to 40%. We calculate that ≈60% of the flux is through the mitochondrial glycerol phosphate dehydrogenase in cells from triiodothyronine-treated rats, compared with ≈15% in cells from the controls. Equal distribution of label between the trioses of glucose was obtained and, because the C3 -C4 spin-spin coupling gives the distribution of labeled carbons in thesame molecule, it was possible to measure the amount of triose from unlabeled fructose incorporated into the glucose labeled at carbons 1, 3, 4, and 6. About 10% of the hexoses had flowed through the pentose cycle and back into the hexose pathway in cells from fasted rats. From the distribution of label at glucose carbons not labeled via the major pathway and from the carbon spin-spin splitting patterns observed, we conclude that transketolase is reversible whereas transaldolase is essentially irreversible in the nonoxidative pentose branch.