Experiments have shown that neocuproine (2,9-dimethyl phenanthroline) blocks the decomposition of RS-NO in cells and tissues. Neocuproine which is often considered to be a selective chelating agent for Cu+ and its effect is often interpreted as proof that the presence of monovalent Cu+ dominates the decomposition of nitrosothiols [20,22]. However, as discussed in Chapter 2, neocuproine interacts with the pool of loosely bound iron as well. EPR spectroscopy has demonstrated that the combination of nitric oxide, ferrous iron and neocuproine results in the formation of dinitrosyl iron complexes (DNIC) with neocuproine ligands. In fact, the presence of NO initiates the binding of neocuproine to ferrous iron. Depending on the pH, two species of DNIC could be distinguished with EPR . The EPR spectra of these species are presented in Chapter 2. It was proved that neocuproine can compete with cysteine for Fe+(NO+)2 moiety in DNIC: The addition of 12.5 mM neocuproine
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