Sweatt Andrew J, Wood Mac, Suryawan Agus, Wallin Reidar, Willingham Mark C, Hutson Susan M
Department of Biochemistry, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA.
Am J Physiol Endocrinol Metab. 2004 Jan;286(1):E64-76. doi: 10.1152/ajpendo.00276.2003. Epub 2003 Sep 9.
We have examined the localization of the first two enzymes in the branched-chain amino acid (BCAA) catabolic pathway: the branched-chain aminotransferase (BCAT) isozymes (mitochondrial BCATm and cytosolic BCATc) and the branched-chain alpha-keto acid dehydrogenase (BCKD) enzyme complex. Antibodies specific for BCATm or BCATc were used to immunolocalize the respective isozymes in cryosections of rat tissues. BCATm was expressed in secretory epithelia throughout the digestive tract, with the most intense expression in the stomach. BCATm was also strongly expressed in secretory cells of the exocrine pancreas, uterus, and testis, as well as in the transporting epithelium of convoluted tubules in kidney. In muscle, BCATm was located in myofibrils. Liver, as predicted, was not immunoreactive for BCATm. Unexpectedly, BCATc was localized in elements of the autonomic innervation of the digestive tract, as well as in axons in the sciatic nerve. The distributions of BCATc and BCATm did not overlap. BCATm-expressing cells also expressed the second enzyme of the BCAA catabolic pathway, BCKD. In selected monkey and human tissues examined by immunoblot and/or immunohistochemistry, BCATm and BCATc were distributed in patterns very similar to those found in the rat. The results show that BCATm is in a position to regulate BCAA availability as protein precursors and anabolic signals in secretory portions of the digestive and other organ systems. The unique expression of BCATc in neurons of the peripheral nervous system, without coexpression of BCKD, raises new questions about the physiological function of this BCAT isozyme.
我们研究了支链氨基酸（BCAA）分解代谢途径中前两种酶的定位：支链氨基转移酶（BCAT）同工酶（线粒体BCATm和胞质BCATc）以及支链α-酮酸脱氢酶（BCKD）复合体。使用针对BCATm或BCATc的特异性抗体对大鼠组织冰冻切片中的相应同工酶进行免疫定位。BCATm在整个消化道的分泌上皮中表达，在胃中表达最为强烈。BCATm在外分泌胰腺、子宫和睾丸的分泌细胞中也强烈表达，在肾曲小管的转运上皮中也有表达。在肌肉中，BCATm位于肌原纤维中。正如预期的那样，肝脏对BCATm没有免疫反应性。出乎意料的是，BCATc定位于消化道自主神经支配的成分以及坐骨神经的轴突中。BCATc和BCATm的分布不重叠。表达BCATm的细胞也表达BCAA分解代谢途径的第二种酶BCKD。在通过免疫印迹和/或免疫组织化学检查的选定猴和人类组织中，BCATm和BCATc的分布模式与在大鼠中发现的非常相似。结果表明，BCATm能够调节BCAA作为蛋白质前体和消化及其他器官系统分泌部分的合成信号的可用性。BCATc在周围神经系统神经元中的独特表达，且不与BCKD共表达，对这种BCAT同工酶的生理功能提出了新的问题。
