Novel detection method of nitric oxide using horseradish peroxidase

Nitric oxide (NO) readily makes corresponding complexes not only with ferrous iron but also with ferric iron. However, NO-ferric complexes of many heme proteins were unstable, while horseradish peroxidase formed the very stable NO-ferric porphyrin complex with a shift of the Soret band of the absorption wavelength from 396.5 nm to 420.0 nm. The concentration of NO in aqueous media could be monitored by measuring the absorption changes, and the detection limit was 10 nM. The simple procedure is convenient for concentration determination of NO solution.