Metges C C, Yu Y M, Cai W, Lu X M, Wong S, Regan M M, Ajami A, Young V R
Laboratory of Human Nutrition, School of Science and Clinical Research Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Am J Physiol Endocrinol Metab. 2000 May;278(5):E868-76. doi: 10.1152/ajpendo.2000.278.5.E868.
L-5-oxoproline (L-5-OP) is an intermediate in glutathione synthesis, possibly limited by cysteine availability. Urinary 5-OP excretion has been proposed as a measure of glycine availability. We investigated whether 5 days of dietary sulfur amino acid (SAA-free) or glycine (Gly-free) restriction affects plasma kinetics of 5-OP and urinary excretion of L- and D-5-OP in 6 healthy men. On day 6, L-5-[1-(13)C]oxoproline and [3,3-(2)H(2)]cysteine were infused intravenously for 8 h (3 h fast/5 h fed). In a control study (adequate amino acid mixture), plasma oxoproline fluxes were 37.8 +/- 13.8 (SD) and 38.4 +/- 14.8 micromol x kg(-1) x h(-1); oxidation accounted for 85% of flux. Cysteine flux was 47.9 +/- 8.5 and 43.2 +/- 8.5 micromol x kg(-1) x h(-1) for fast and fed phases, respectively. Urinary excretion of L- and D-5-OP was 70 +/- 34 and 31.1 +/- 13.3 micromol/mmol creatinine, respectively, during days 3-5, and 46.4 +/- 13.9 and 22.4 +/- 8.3 micromol/mmol over the 8-h tracer study. The 5-OP flux for the Gly-free diet was higher (P = 0. 018) and tended to be higher for the SAA-free diet (P = 0.057) when compared with the control diet. Oxidation rates were higher on the Gly-free (P = 0.005) and SAA-free (P = 0.03) diets. Cysteine fluxes were lower on the the Gly-free (P = 0.01) and the SAA-free diets (P = 0.001) compared with the control diet. Rates of L-5-OP excretion were unchanged by withdrawal of SAA or Gly for 5 days but increased on day 6 (P = 0.005 and P = 0.019, respectively). Thus acute changes in the dietary availability of SAA and Gly alter oxoproline kinetics and urinary 5-OP excretion.
L-5-氧代脯氨酸（L-5-OP）是谷胱甘肽合成的中间产物，可能受半胱氨酸可用性的限制。尿中5-OP排泄已被提议作为甘氨酸可用性的一种衡量指标。我们研究了6名健康男性5天的饮食中限制硫氨基酸（无硫氨基酸）或甘氨酸（无甘氨酸）是否会影响5-OP的血浆动力学以及L-和D-5-OP的尿排泄。在第6天，静脉输注L-5-[1-(13)C]氧代脯氨酸和[3,3-(2)H(2)]半胱氨酸8小时（禁食3小时/进食5小时）。在一项对照研究（充足的氨基酸混合物）中，血浆氧代脯氨酸通量分别为37.8±13.8（标准差）和38.4±14.8微摩尔·千克(-1)·小时(-1)；氧化占通量的85%。半胱氨酸通量在禁食期和进食期分别为47.9±8.5和43.2±8.5微摩尔·千克(-1)·小时(-1)。在第3至5天，L-和D-5-OP的尿排泄分别为70±34和31.1±13.3微摩尔/毫摩尔肌酐，在8小时的示踪研究中分别为46.4±13.9和22.4±8.3微摩尔/毫摩尔。与对照饮食相比，无甘氨酸饮食的5-OP通量更高（P = 0.018），无硫氨基酸饮食的5-OP通量有升高趋势（P = 0.057）。无甘氨酸（P = 0.005）和无硫氨基酸（P = 0.03）饮食的氧化率更高。与对照饮食相比，无甘氨酸（P = 0.01）和无硫氨基酸饮食（P = 0.001）的半胱氨酸通量更低。5天不摄入硫氨基酸或甘氨酸，L-5-OP排泄率不变，但在第6天增加（分别为P = 0.005和P = 0.019）。因此，饮食中硫氨基酸和甘氨酸可用性的急性变化会改变氧代脯氨酸动力学和尿中5-OP排泄。
