Biolo G, Fleming R Y, Maggi S P, Wolfe R R
Department of Internal Medicine, University of Texas Medical Branch, Galveston.
Am J Physiol. 1995 Jan;268(1 Pt 1):E75-84. doi: 10.1152/ajpendo.1995.268.1.E75.
We have used stable isotopic tracers of amino acids to measure in vivo transmembrane transport of phenylalanine, leucine, lysine, alanine, and glutamine as well as the rates of intracellular amino acid appearance from proteolysis, de novo synthesis, and disappearance to protein synthesis in human skeletal muscle. Calculations were based on data obtained by the arteriovenous catheterization of the femoral vessels and muscle biopsy. We found that the fractional contribution of transport from the bloodstream to the total intracellular amino acid appearance depends on the individual amino acid, varying between 0.63 +/- 0.02 for phenylalanine and 0.22 +/- 0.02 for alanine. Rates of alanine and glutamine de novo synthesis were approximately eight and five times their rate of appearance from protein breakdown, respectively. The model-derived rate of protein synthesis was highly correlated with the same value calculated by means of the tracer incorporation technique. Furthermore, amino acid transport rates were in the range expected from literature values. Consequently, we conclude that our new model provides a valid means of quantifying the important aspects of protein synthesis, breakdown, and amino acid transport in human subjects.
我们使用氨基酸的稳定同位素示踪剂来测量人体骨骼肌中苯丙氨酸、亮氨酸、赖氨酸、丙氨酸和谷氨酰胺的体内跨膜转运，以及蛋白质水解、从头合成和蛋白质合成中氨基酸消失后细胞内氨基酸出现的速率。计算基于通过股血管动静脉插管和肌肉活检获得的数据。我们发现，从血液到细胞内氨基酸总出现量的转运分数贡献取决于个别氨基酸，苯丙氨酸为0.63±0.02，丙氨酸为0.22±0.02。丙氨酸和谷氨酰胺的从头合成速率分别约为其从蛋白质分解中出现速率的8倍和５倍。模型推导的蛋白质合成速率与通过示踪剂掺入技术计算的相同值高度相关。此外，氨基酸转运速率在文献值预期的范围内。因此，我们得出结论，我们的新模型提供了一种有效的方法来量化人体蛋白质合成、分解和氨基酸转运的重要方面。
