Bec N, Mayer B, Schmidt P P, Andersson K K, Lange R
lnstitut für Pharmakologie und Toxikologie, Karl-Franzens-Universität, Graz, Austria.
J Inorg Biochem. 2000 Aug 31;81(3):207-11. doi: 10.1016/s0162-0134(00)00104-5.
We have studied the reaction of reduced nitric-oxide synthase (NOS) with molecular oxygen at -30 degrees C. In the first reaction cycle (from L-Arg to hydroxy-L-Arg), an oxygen adduct complex formed rapidly. Experiments in the absence of the reductase domain demonstrated that this complex was then further reduced by one electron stemming from the cofactor tetrahydrobiopterin (BH4). Spectral evidence suggested an iron(IV) porphyrin pi-cation radical as an intermediate. The nature of the oxidized BH4 was identified by EPR as a BH3* radical. Within the second cycle (from hydroxy-L-Arg to citrulline and NO), an iron(III)-NO complex could be identified clearly by its spectral characteristics. The strict requirement of BH4 for its formation suggests that BH4 plays a redox role, although transient, also in the second reaction cycle.
我们研究了还原型一氧化氮合酶（NOS）在-30℃下与分子氧的反应。在第一个反应循环（从L-精氨酸到羟基-L-精氨酸）中，迅速形成了一种氧加合物复合物。在没有还原酶结构域的情况下进行的实验表明，该复合物随后被来自辅因子四氢生物蝶呤（BH4）的一个电子进一步还原。光谱证据表明，一种铁（IV）卟啉π-阳离子自由基作为中间体。通过电子顺磁共振（EPR）确定氧化型BH4的性质为BH3*自由基。在第二个循环（从羟基-L-精氨酸到瓜氨酸和一氧化氮）中，铁（III）-一氧化氮复合物可通过其光谱特征清楚地识别。BH4对其形成的严格要求表明，BH4在第二个反应循环中也发挥了氧化还原作用，尽管是短暂的。
