Flam Brenda R, Eichler Duane C, Solomonson Larry P
Department of Internal Medicine, College of Medicine, University of South Florida, 12901 Bruce B. Downs Boulevard, Tampa, FL 33612-4799, USA.
Nitric Oxide. 2007 Nov-Dec;17(3-4):115-21. doi: 10.1016/j.niox.2007.07.001. Epub 2007 Aug 3.
Nitric oxide (NO) is an important vasorelaxant produced along with L-citrulline from L-arginine in a reaction catalyzed by endothelial nitric oxide synthase (eNOS). Previous studies suggested that the recycling of L-citrulline to L-arginine is essential for NO production in endothelial cells. However, there is no direct evidence demonstrating the degree to which the recycling of L-citrulline to L-arginine is coupled to NO production. We hypothesized that the amount of NO formed would be significantly higher than the amount of L-citrulline formed due to the efficiency of L-citrulline recycling via the citrulline-NO cycle. To test this hypothesis, endothelial cells were incubated with [14C]-L-arginine and stimulated by various agents to produce NO. The extent of NO and [14C]-L-citrulline formation were simultaneously determined. NO production exceeded apparent L-citrulline formation of the order of 8 to 1, under both basal and stimulated conditions. As further support, alpha-methyl-DL-aspartate, an inhibitor of argininosuccinate synthase (AS), a component of the citrulline-NO cycle, inhibited NO production in a dose-dependent manner. The results of this study provide evidence for the essential and efficient coupling of L-citrulline recycling, via the citrulline-NO cycle, to endothelial NO production.
一氧化氮（NO）是一种重要的血管舒张剂，它与L-瓜氨酸一起由L-精氨酸在内皮型一氧化氮合酶（eNOS）催化的反应中生成。先前的研究表明，L-瓜氨酸向L-精氨酸的再循环对于内皮细胞中NO的生成至关重要。然而，尚无直接证据证明L-瓜氨酸向L-精氨酸的再循环与NO生成的耦合程度。我们推测，由于通过瓜氨酸-NO循环进行L-瓜氨酸再循环的效率，生成的NO量将显著高于生成的L-瓜氨酸量。为了验证这一假设，将内皮细胞与[14C]-L-精氨酸一起孵育，并用各种试剂刺激以产生NO。同时测定NO和[14C]-L-瓜氨酸的生成程度。在基础和刺激条件下，NO的生成均超过明显的L-瓜氨酸生成量，比例约为8比1。作为进一步的支持，精氨酸琥珀酸合成酶（AS）（瓜氨酸-NO循环的一个组成部分）的抑制剂α-甲基-DL-天冬氨酸以剂量依赖的方式抑制NO的生成。本研究结果为通过瓜氨酸-NO循环进行的L-瓜氨酸再循环与内皮细胞NO生成之间的必要且有效的耦合提供了证据。
