饮食蛋白质水平调节大鼠线粒体支链氨基转移酶的表达。

Dietary protein level regulates expression of the mitochondrial branched-chain aminotransferase in rats.

作者信息

Torres N, López G, De Santiago S, Hutson S M, Tovar A R

机构信息

Departamento de Fisiología de la Nutrición, Instituto Nacional de Nutrición, México D.F., 14000, Mexico.

出版信息

J Nutr. 1998 Aug;128(8):1368-75. doi: 10.1093/jn/128.8.1368.

DOI:10.1093/jn/128.8.1368

PMID:9687558

Abstract

The first step in the degradation of branched-chain amino acids (BCAA) is transamination catalyzed by the branched-chain aminotransferase (BCAT), which is located in extrahepatic tissues. Studies of the effect of dietary protein on BCAT activity have given contradictory results. Therefore, we established the levels of BCAT activity and mitochondrial BCAT (BCATm) mRNA expression in different organs and tissues of rats. We then determined the effect of different levels of dietary protein in well-nourished rats, the effect of feeding a 0.5% casein diet for 5 wk (protein-malnourished rats) and nutritional rehabilitation of these rats with different levels of dietary protein on BCAT activity and BCATm mRNA expression in selected tissues. Finally, the response of tissue BCAT activity and BCATm mRNA levels in rats fed a 10% casein diet and injected with glucagon (4 d) or hydrocortisone (7 d) was determined. The highest concentration of BCATm mRNA was found in stomach, followed by kidney, heart, muscle, brain, skin and lung. Low levels were found in intestine, and no BCATm mRNA was detectable in liver. Although BCAT activity was significantly higher in muscle, kidney and brain from rats adapted to consume a 50% casein diet for 7 h/d for 10 d than in rats fed 6, 18 or 35% casein diets, only muscle had significantly higher levels of BCATm mRNA. In protein-malnourished rats, BCAT activity and BCATm mRNA expression in kidney, muscle and heart were not different from those of rats with free access to an 18% casein diet. Nutritional rehabilitation of the protein-malnourished rats with 50% casein for 21 d significantly increased the BCAT activity and BCATm mRNA expression in muscle. Neither hydrocortisone nor glucagon injection affected BCAT activity or BCATm mRNA concentrations in rat kidney, muscle or heart. We conclude that the nutritional regulation of BCATm is extrahepatic, tissue specific and may involve transcriptional and post-translational mechanisms.

摘要

支链氨基酸（BCAA）降解的第一步是由位于肝外组织的支链氨基转移酶（BCAT）催化的转氨作用。关于膳食蛋白质对BCAT活性影响的研究结果相互矛盾。因此，我们测定了大鼠不同器官和组织中BCAT活性及线粒体BCAT（BCATm）mRNA表达水平。然后，我们确定了营养良好的大鼠摄入不同水平膳食蛋白质的影响、喂食0.5%酪蛋白饮食5周（蛋白质营养不良大鼠）的影响以及用不同水平膳食蛋白质对这些大鼠进行营养康复后对所选组织中BCAT活性和BCATm mRNA表达的影响。最后，测定了喂食10%酪蛋白饮食并注射胰高血糖素（4天）或氢化可的松（7天）的大鼠组织BCAT活性和BCATm mRNA水平的反应。发现BCATm mRNA浓度最高的是胃，其次是肾脏、心脏、肌肉、大脑、皮肤和肺。在肠道中发现的水平较低，在肝脏中未检测到BCATm mRNA。尽管适应每天7小时食用50%酪蛋白饮食10天的大鼠肌肉、肾脏和大脑中的BCAT活性显著高于喂食6%、18%或35%酪蛋白饮食的大鼠，但只有肌肉中的BCATm mRNA水平显著更高。在蛋白质营养不良的大鼠中，肾脏、肌肉和心脏中的BCAT活性和BCATm mRNA表达与自由摄入18%酪蛋白饮食的大鼠没有差异。用50%酪蛋白对蛋白质营养不良的大鼠进行21天的营养康复显著增加了肌肉中的BCAT活性和BCATm mRNA表达。注射氢化可的松或胰高血糖素均未影响大鼠肾脏、肌肉或心脏中的BCAT活性或BCATm mRNA浓度。我们得出结论，BCATm的营养调节是肝外的、组织特异性的，可能涉及转录和翻译后机制。