Darling P B, Grunow J, Rafii M, Brookes S, Ball R O, Pencharz P B
The Research Institute, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
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.
苏氨酸脱氢酶（TDG）途径是苏氨酸降解的一条重要途径，在实验动物中可产生甘氨酸，但在人类中尚未得到准确的定量。因此，在6名健康成年男性中，通过4小时持续输注L-[1-(13)C]苏氨酸和[(15)N]甘氨酸，研究了大量过量的膳食苏氨酸（以游离氨基酸形式给予（+Thr）或作为蛋白质的组成成分给予（+P-Thr））对苏氨酸分解代谢为CO(2)和甘氨酸的影响。采用气相色谱-燃烧同位素比率质谱法测定由标记苏氨酸产生的[(13)C]甘氨酸。与对照组相比，+Thr和+P-Thr饮食的苏氨酸摄入量更高（分别为126、126和50微摩尔·千克(-1)·小时(-1)，标准差8，P<0.0001）。与对照组相比，+Thr和+P-Thr组受试者中苏氨酸氧化为CO(2)的量增加了三倍（分别为49、45和15微摩尔·千克(-1)·小时(-1)，标准差6，P<0.0001）。与对照组相比，+Thr和+P-Thr组中苏氨酸转化为甘氨酸的量有升高趋势（分别为3.5、3.4和1.6微摩尔·千克(-1)·小时(-1)，标准差1.3，P = 0.06）。TDG途径仅占总苏氨酸分解代谢的7-11%，因此在成年人体内是一条次要途径。
