Wagenmakers A J
Department of Human Biology, University of Limburg, Maastricht, The Netherlands.
Int J Sports Med. 1992 Oct;13 Suppl 1:S110-3. doi: 10.1055/s-2007-1024611.
Recent investigations from our and other laboratories indicate that glycogen is a carbon-chain precursor in muscle for the synthesis of TCA cycle intermediates and glutamine. During intense exercise and in conditions of a relative lack of energy (hypoxia, trauma, sepsis) the metabolism of branched-chain amino acids (BCAA) is accelerated in muscle. In the primary BCAA aminotransferase reaction 2-oxoglutarate is used as amino-group acceptor (putting a carbon-drain on the TCA cycle) under formation of glutamate. Glutamate will subsequently react with ammonia, generated in the AMP deaminase reaction or by deamination of amino acids, under formation of glutamine in a reaction catalysed by glutamine synthetase (glutamate + ammonia + ATP--> glutamine + ADP). Muscle glycogen stores may be smaller or less available at high altitude. It is hypothesized that this will lead to premature fatigue (due to both a lack of fuel and of TCA cycle carbon-precursor) and to a reduction in the synthesis rate of glutamine. A chronic reduction in the synthesis rate of glutamine during a long term stay at high altitude on its turn may lead to gut atrophy, bacterial translocation, endotoxemia, muscle protein catabolism and a weakened immune status.
我们实验室及其他实验室最近的研究表明，糖原是肌肉中用于合成三羧酸循环中间产物和谷氨酰胺的碳链前体。在剧烈运动以及能量相对缺乏（缺氧、创伤、脓毒症）的情况下，肌肉中支链氨基酸（BCAA）的代谢会加速。在支链氨基酸转氨酶的主要反应中，2-酮戊二酸用作氨基受体（使三羧酸循环出现碳流失），生成谷氨酸。随后，谷氨酸会与在AMP脱氨酶反应中产生或由氨基酸脱氨基作用产生的氨发生反应，在谷氨酰胺合成酶催化的反应中生成谷氨酰胺（谷氨酸+氨+ATP→谷氨酰胺+ADP）。在高海拔地区，肌肉糖原储备可能较少或可用性较低。据推测，这将导致过早疲劳（由于缺乏燃料和三羧酸循环碳前体）以及谷氨酰胺合成速率降低。长期呆在高海拔地区时，谷氨酰胺合成速率的长期降低反过来可能导致肠道萎缩、细菌移位、内毒素血症、肌肉蛋白分解代谢以及免疫状态减弱。
