NITRIC OXIDE INHIBITION OF TARGET ENZYMES

一氧化氮(NO)是一种双原子自由基，可以很容易地扩散到生物膜上。NO控制和影响许多关键的生理过程。NO控制的生理反应最典型的例子包括血管扩张和调节正常血管张力，抑制血小板聚集，神经元传递和细胞停滞。可以介导这种细胞抑制作用的NO的一个细胞靶点是核糖核苷酸还原酶(RNR)。预计NO还会影响硫氧还蛋白和硫氧还蛋白还原酶等相关蛋白质。抑制这些蛋白质也可能导致细胞停滞。对靶细胞DNA合成的抑制已有报道，但其抑制机制尚不清楚。因此，本研究的目的是确定NO抑制大肠杆菌核糖核苷酸还原酶(RNR)的分子机制以及NO对相关蛋白质的影响。这些研究将利用克隆和表达的蛋白质来源来解决以下特定目标：(L)NO对硫氧还蛋白(Trx)和硫氧还蛋白还原酶(TR)的影响；(2)NO对RNR酶促周转的影响；(3)NO对RNR铁中心组装的影响。

Nitric oxide (NO) is a diatomic radical which can diffuse readily across biological membranes. NO controls and influences a number of critical physiological processes. The best characterized examples of physiological responses controlled by NO include vasodilation and regulation of normal vascular tone, inhibition of platelet aggregation, neuronal transmission and cytostasis. One proposed cellular target for NO which could mediate such cytostatic effects is ribonucleotide reductase (RNR). NO would also be expected to influence related proteins such thioredoxin and thioredoxin reductase. Inhibition of these proteins would also be expected to induce cytostasis. The inhibition of DNA synthesis in target cells has been reported, however, the mechanism of the inhibition is unknown. The goal of the proposed studies, therefore, is to determine the molecular' mechanism of NO inhibition of E. coli ribonucleotide reductase (RNR) and the effect on NO on related proteins. The studies will use cloned and expressed sources of the proteins to address the following specific aims: (l) the effect of NO on thioredoxin (Trx) and thioredoxin reductase (TR), (2) the effect of NO on enzymatic turnover of RNR, (3) the effect of NO on the assembly of the iron center of RNR.