Mechanism of inhibition of catalase by nitro and nitroso compounds

Abstract

Dinitrosyl iron complexes (DNIC) with thiolate ligands and S-nitrosothiols, which are NO and NO+ donors, share the earlier demonstrated ability of nitrite for inhibition of catalase. The efficiency of inhibition sharply (by several orders in concentration of these agents) increases in the presence of chloride, bromide, and thiocyanate. The nitro compounds tested--nitroarginine, nitroglycerol, nitrophenol, and furazolidone--gained the same inhibition ability after incubation with ferrous ions and thiols. This is probably the result of their transformation into DNIC. None of these substances lost the inhibitory effect in the presence of the well known NO scavenger oxyhemoglobin. This fact suggests that NO+ ions rather than neutral NO molecules are responsible for the enzyme inactivation due to nitrosation of its structures. The enhancement of catalase inhibition in the presence of halide ions and thiocyanate might be caused by nitrosyl halide formation. The latter protected nitrosonium ions against hydrolysis, thereby ensuring their transfer to the targets in enzyme molecules. The addition of oxyhemoglobin plus iron chelator o-phenanthroline destroying DNIC sharply attenuated the inhibitory effect of DNIC on catalase. o-Phenanthroline added alone did not influence this effect. Oxyhemoglobin is suggested to scavenge nitrosonium ions released from decomposing DNIC, thereby preventing catalase nitrosation. The mixture of oxyhemoglobin and o-phenanthroline did not affect the inhibitory action of nitrite or S-nitrosothiols on catalase.

Possible Mechanism of Generation of Nitrite and Non-Thiolate Nitroso Compounds in Blood Plasma during Inflammatory Processes

“…Titov In accordance to our data, the majority of living tissues, including the blood, normally contain minimal concentration of nitrite (<100 nM) [3,11]. The data on the presence of nitrite in blood plasma of healthy volunteers in higher doses can be stipulated by low selectivity of using methods [3,11,12]. Several investigations show increased level of nitrite in the blood of patients with infl ammatory processes [4][5][6].…”

“…The levels of nitro and nitroso compounds were determined using an enzyme sensor described in our previous studied [3,11,12] and based on inhibition of catalase with nitroso compounds in the presence of haloid ions. Other known inhibitors of catalase do not manifest this effect and do not exist in biological samples in high concentrations, so they cannot produce artifi cial data [11,12]. Dinitrosyl iron complexes with thiolate ligands (DNIC/GSH) lose inhibiting ability in the medium containing iron chelators (o-phenanthroline, EDTA) and NO trap (oxyhemoglobin), which capture NO.…”

“…Dinitrosyl iron complexes with thiolate ligands (DNIC/GSH) lose inhibiting ability in the medium containing iron chelators (o-phenanthroline, EDTA) and NO trap (oxyhemoglobin), which capture NO. S-nitrosothiols (RSNO) are converted into DNIC/SH under the infl uence of iron (II) and thiols [11,12] and acquiring their properties. NO 2 and RNNO practically do not produce DNIC/SH in neutral medium and preserve their inhibiting properties after consequent addition of iron (II), glutathione, NO trap, and iron chelator [11,12].…”

“…S-nitrosothiols (RSNO) are converted into DNIC/SH under the infl uence of iron (II) and thiols [11,12] and acquiring their properties. NO 2 and RNNO practically do not produce DNIC/SH in neutral medium and preserve their inhibiting properties after consequent addition of iron (II), glutathione, NO trap, and iron chelator [11,12]. Nitrosyl iron complexes without thiols (Fe-(NO)n) serve as agents acquiring the properties of DNIC/SH after addition of glutathione to the reaction medium [11,12].…”

“…Preliminary treatment of a sample is not necessary during this method, its sensitivity is 40 nM [11]. Nitrite level was additionally estimated by the classical Griess method [12].Blood samples were taken from volunteers. Blood clotting was prevented by adding heparin (0.1 ml 1% solution per 10 ml of the blood).…”