Characterization of Iron Dinitrosyl Species Formed in the Reaction of Nitric Oxide with a Biological Rieske Center

摘要

Reactions of nitric oxide with cysteine-ligated iron-sulfur cluster proteins typically result in disassembly of the iron-sulfur core and formation of dinitrosyl iron complexes (DNICs). Here we report the first evidence that DNICs also form in the reaction of NO with Rieske-type [2Fe-2S] clusters. Upon treatment of a Rieske protein, component C of toluene/o-xylene monooxygenase (ToMOC) from Pseudomonas sp. OX1, with a slight excess of NO (g) or NO-generators S-nitroso-N-acetyl-D,L-pencillamine (SNAP) and diethylamine NONOate (DEANO), the absorbance bands of the [2Fe-2S] cluster are epxtinguished and replaced by a new feature that slowly grows in at 367 nm. Analysis of the reaction products by EPR, Mössbauer, and NRVS spectroscopy reveals that the primary product of the reaction is a thiolate-bridged diiron tetranitrosyl species, [Fe2(μ-SCys)2(NO)4] having a Roussin's red ester (RRE) formula, and that mononuclear DNICs account for only a minor fraction of nitrosylated iron. Reduction of this RRE reaction product with sodium dithionite produces the one-electron reduced Roussin's red ester (rRRE) having absorbtions at 640 and 960 nm. These results demonstrate that NO reacts readily with Rieske centers in protein and suggest that dinuclear RRE species, not mononuclear DNICs, may be the primary iron dinitrosyl species responsible for the pathological and physiological effects of nitric oxide in such systems in biology.