Threonine dehydrogenase is a minor degradative pathway of threonine catabolism in adult humans

Am J Physiol Endocrinol Metab. 2000 May;278(5):E877-84. doi: 10.1152/ajpendo.2000.278.5.E877.


The threonine dehydrogenase (TDG) pathway is a significant route of threonine degradation, yielding glycine in experimental animals, but has not been accurately quantitated in humans. Therefore, the effect of a large excess of dietary threonine, given either as free amino acid (+Thr) or as a constituent of protein (+P-Thr), on threonine catabolism to CO(2) and to glycine was studied in six healthy adult males using a 4-h constant infusion of L-[1-(13)C]threonine and [(15)N]glycine. Gas chromatography-combustion isotope ratio mass spectrometry was used to determine [(13)C]glycine produced from labeled threonine. Threonine intakes were higher on +Thr and +P-Thr diets compared with control (126, 126, and 50 micromol x kg(-1) x h(-1), SD 8, P < 0.0001). Threonine oxidation to CO(2) increased threefold in subjects on +Thr and +P-Thr vs. control (49, 45, and 15 micromol x kg(-1) x h(-1), SD 6, P < 0.0001). Threonine conversion to glycine tended to be higher on +Thr and +P-Thr vs. control (3.5, 3.4, and 1.6 micromol x kg(-1) x h(-1), SD 1.3, P = 0.06). The TDG pathway accounted for only 7-11% of total threonine catabolism and therefore is a minor pathway in the human adult.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Alcohol Oxidoreductases / metabolism*
  • Aminobutyrates / blood
  • Carbon Isotopes
  • Dietary Proteins / administration & dosage
  • Energy Metabolism
  • Gas Chromatography-Mass Spectrometry
  • Glycine / administration & dosage
  • Glycine / blood
  • Humans
  • Male
  • Nitrogen Isotopes
  • Oxidation-Reduction
  • Threonine / administration & dosage
  • Threonine / blood*


  • Aminobutyrates
  • Carbon Isotopes
  • Dietary Proteins
  • Nitrogen Isotopes
  • Threonine
  • alpha-aminobutyric acid
  • Alcohol Oxidoreductases
  • L-threonine 3-dehydrogenase
  • Glycine