Nitric oxide initiates iron binding to neocuproine

It was demonstrated that two species of paramagnetic dinitrosyl iron comple x (DNIC) with neocuproine form under the following conditions: in ad dition of neocuproine to a solution of DNIC with phosphate; in gaseous NO treatme nt of a mixture of Fe2+ + neocuproine aqueous solutions at pH 6.5-8; and in addition of Fe2+ - citrate complex + neocuproine to a S-nitrosocysteine (c ys-NO) solution. The first form of DNIC with neocuproine is characterized b y an EPR signal with g-factor values of 2.087, 2.055, and 2.025, when it is recorded at 77K. At room temperature, the complex displays a symmetric sin glet at g = 2.05. The second form of DNIC with neocuproine gives an EPR sig nal with g-factor values of 2.042, 2.02, and 2.003, which can be recorded a t a low temperature only. The revealed complexes are close to DNIC with cys teine in their stability. The ability of neocuproine to bind Fe2+ in the pr esence of NO with formation of paramagnetic DNICs warrants critical reevalu ation of the statement that neocuproine is only able to bind Cu+ ions. It w as suggested that the observed affinity of neocuproine to iron was due to t ransition of Fe2+ in DNIC with neocuproine to Fe+. In experiments on cys-NO , it was shown that the stabilizing effect of neocuproine on this compound could be due to neocuproine binding to the iron catalyzing decomposition of cys-NO. (C) 2001 Academic Press.