Nitric oxide (NO) is a free radical and signaling molecule that plays an important role in vasodilation, immune system function, apoptosis and many other physiological and pathological processes. Nitric oxide is generated either via the oxidation of L-arginine by NO synthases (NOSs) or the reduction of dietary Nitrite (NO2) and Nitrate (NO3) by various metal-containing proteins. Nitric oxide is an unstable molecule that quickly degrades, which makes it challenging for direct detection methods. However, as the NO2 and NO3 are the stable metabolites of NO oxidation, their concentration is conveniently measured via colorimetric methods and reported as the total NO content in biological samples.
The ZellX® Nitric Oxide (NO) assay kit is designed to quantitatively measure the total NO content, i.e. the sum of Nitrite (NO2) and Nitrate (NO3) in a variety of samples. The total Nitric Oxide kit has two assay options: For NO2 Determination: Samples are mixed with Color Reagents A and B, and incubated at room temperature for 5 minutes and read at 540-570 nm to quantify the endogenous NO2 level. For total NO Determination: As mentioned above, the total NO content is derived from the sum of NO2 and NO3, for which, endogenous NO3 is first reduced to NO2 with Nitrate Reductase and NADH, and then processed similar to the first option. To obtain the NO3 concentration, endogenous NO2 is subtracted from the total NO value.