Freeman T L, Mailliard M E
Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska, USA.
Biochem Biophys Res Commun. 2000 Nov 30;278(3):729-32. doi: 10.1006/bbrc.2000.3876.
The recent cloning of ATA2, a cDNA displaying characteristics identical to the System A transporter, has provided the first molecular tool for study of System A-mediated amino acid transport in liver. Despite the 233 +/- 9 and 472 +/- 11% increase in System A transport activity following partial hepatectomy at 6 and 12 h, respectively, the steady-state level of ATA2 mRNA did not show a corresponding marked increase. Examination of the kinetic properties of System A following partial hepatectomy revealed a K(m) of 0.26 +/- 0.04 mM which is consistent with the reported K(m) for ATA2. These results indicate that a System A transporter present in regenerating liver and ATA2 are identical, but that the increase in System A activity following partial hepatectomy does not result from an increase in steady-state levels of ATA2 mRNA. These observations suggest that ATA2-mediated transport of amino acids is regulated at the posttranscriptional level.
ATA2（一种显示出与A系统转运体相同特征的cDNA）最近被克隆出来，这为研究肝脏中A系统介导的氨基酸转运提供了首个分子工具。尽管在部分肝切除术后6小时和12小时，A系统转运活性分别增加了233±9%和472±11%，但ATA2 mRNA的稳态水平并未出现相应的显著增加。对部分肝切除术后A系统的动力学特性进行检测发现，其米氏常数（K(m)）为0.26±0.04 mM，这与报道的ATA2的K(m)一致。这些结果表明，再生肝脏中存在的A系统转运体与ATA2相同，但部分肝切除术后A系统活性的增加并非源于ATA2 mRNA稳态水平的升高。这些观察结果提示，ATA2介导的氨基酸转运在转录后水平受到调控。
