'NO' News is 'NOS' News: Direct Electrochemical Investigation of Nitric Oxide Biosynthesis

摘要

Nitric oxide (NO), an important physiologic player, is synthesized in vivo by nitric oxide synthases (NOSs). NO plays critical role in vasodilation, neurotransmission, and in host-defense. NOSs are P450-type enzymes and carry a five-electron oxidation of the amino- acid arginine to NO and citrulline by a unique two-step activation of molecular oxygen. Evidence suggests that the activation is assisted by tetrahydrobiopterin, a necessary cofactor in the NOS function. A number of issues regarding the function of NOS including electron transport and oxygen activation in NOSs are yet to be resolved. Voltammetry in thin films is an excellent technique to perform fast and direct electron transfer to redox active metalloenzymes such as the NOS. In the present study we use heme-domains of nitric oxide synthase embedded in surfactant films to investigate the electrochemical properties of the heme in NOS and the effect of substrate and cofactor binding. Electrocatalytic oxygen activation and enzyme full turnover can also be addressed using the same technology. We will summarize and discuss significant results of our work in this area and will show how direct electrochemical activation of NOS heme-domain can reveal more about the mechanism of critical steps of the NOS catalysis.