Lundholm K, Ternell M, Zachrisson H, Moldawer L, Lindström L
Department of Surgery, Sahlgrenska Hospital, Gothenburg, Sweden.
Acta Physiol Scand. 1991 Feb;141(2):207-19. doi: 10.1111/j.1748-1716.1991.tb09069.x.
Controversy exists regarding the validity of various techniques for estimating rates of protein synthesis in vivo. In the present report, we have compared estimates of hepatic protein synthesis in normal mice with a pulse labelling of [1-14C]leucine and calculated hepatic protein synthetic rates in a conventional two-pool model and in a five-pool compartment analysis. Results obtained with pulse labelling were also compared to those obtained in animals receiving a flooding dose of 1.5 mumol L-phenylalanine and 0.4 microCi [U-14C]phenylalanine per gram of body weight or 1.0 mumol L-leucine and 0.4 microCi [l-14C]leucine per gram of body weight. Estimates of protein synthesis were calculated with plasma free amino acid, liver acid-soluble fraction and acylated tRNA specific radioactivities as being representative of the precursor pool for protein synthesis. Rates of hepatic protein synthesis obtained with pulse labelling and either leu-tRNA or acid-soluble fractions of liver leucine as the precursor for protein synthesis gave similar results (37 +/- 5 vs 42 +/- 5% per day) in a two-pool model, but disagreed in a five-pool model (37 +/- 5 vs 6 +/- 2% per day). Estimates based on plasma enrichment in leucine were only one fifth of values obtained with tRNA in labelling experiments. When the plasma pool with tracer amino acids was used to indicate the precursor labelling of protein synthesis, values obtained with the flooding dose of either phenylalanine or leucine agreed with those obtained with pulse labelling and enrichment in tRNA (30 +/- 3 nmol min-1 vs 28 +/- 4 nmol min-1); with however no agreement when the enrichment in the liver mixed tissue pool was used (76 +/- 5 nmol min-1). Complete equilibration of the amino acid pools did not occur despite flooding. Therefore, the flooding technique may only represent an approximate method to measure protein synthesis in vivo, although it gives absolute values that agree well with results from labelling techniques based on tRNA enrichment provided the plasma pool is used as the precursor enrichment.
关于体内蛋白质合成速率的各种估算技术的有效性存在争议。在本报告中，我们比较了正常小鼠肝脏蛋白质合成的估算值，这些估算值通过用[1-¹⁴C]亮氨酸进行脉冲标记获得，并在传统的双池模型和五池隔室分析中计算肝脏蛋白质合成速率。脉冲标记获得的结果还与接受每克体重1.5 μmol L-苯丙氨酸和0.4 μCi [U-¹⁴C]苯丙氨酸或每克体重1.0 μmol L-亮氨酸和0.4 μCi [l-¹⁴C]亮氨酸的冲击剂量的动物所获得的结果进行了比较。蛋白质合成的估算值是根据血浆游离氨基酸、肝脏酸溶性部分和酰化tRNA的比放射性来计算的，这些被视为蛋白质合成前体池的代表。在双池模型中，以脉冲标记以及亮氨酰-tRNA或肝脏亮氨酸的酸溶性部分作为蛋白质合成前体获得的肝脏蛋白质合成速率给出了相似的结果（每天37±5%对42±5%），但在五池模型中不一致（每天37±5%对6±2%）。基于亮氨酸血浆富集的估算值仅为标记实验中用tRNA获得值的五分之一。当用含有示踪氨基酸的血浆池来指示蛋白质合成的前体标记时，用苯丙氨酸或亮氨酸的冲击剂量获得的值与用脉冲标记和tRNA富集获得的值一致（30±3 nmol min⁻¹对28±4 nmol min⁻¹）；然而，当使用肝脏混合组织池中的富集时则不一致（76±5 nmol min⁻¹）。尽管进行了冲击，氨基酸池并未完全达到平衡。因此，冲击技术可能只是一种测量体内蛋白质合成的近似方法，尽管它给出的绝对值与基于tRNA富集的标记技术的结果非常吻合，前提是将血浆池用作前体富集。
