Complexes of ferriheme nitrophorin 4 with low-molecular weight thiol(ate)s occurring in blood plasma.

Complexes of ferriheme nitrophorin 4 with low-molecular weight thiol(ate)s occurring in blood plasma. J Inorg Biochem. 2013 May;122:38-48 Authors: He C, Nishikawa K, Erdem ÖF, Reijerse E, Ogata H, Lubitz W, Knipp M Abstract Nitrophorins are proteins occurring in the saliva of the blood-sucking insect Rhodnius prolixus to carry NO as a vasodilator and blood-coagulation inhibitor into the victim's tissue. It was suggested that the rate of NO release can be enhanced by the blood-plasma component L-cysteine [J.M.C.Ribeiro, Insect Biochem. Mol. Biol. 26 (1996) 899-905]. However, the mechanism of the reaction is not clear. In the attempt to exploit the reaction in detail, complexes of nitrophorin 4 (NP4) with the thiols 2-mercaptoethanol, L-cysteine, and L-homocysteine and with HS(-) were formed and characterized under anaerobic conditions using absorption spectroscopy, X-ray crystallography, and EPR spectroscopy. In contrast to met-myoglobin, which is reduced by L-cysteine, all four compounds form low-spin Fe(III) complexes with NP4. The weak equilibration constants (167-5200 M(-1)) neither support significant complexation nor the simple displacement of NO in vivo. Both amino acid based thiols form additional H-bonds with side chains of the heme pocket entry. Glutathione and L-methionine did not form a complex, indicating the specificity of the complexes with L-cysteine and L-homocysteine. Continuous wave EPR spectroscopy reveals the simultaneous ...
Source: Journal of Inorganic Biochemistry - Category: Biochemistry Authors: Tags: J Inorg Biochem Source Type: research