Lactoperoxidase-Catalyzed Oxidation of Thiocyanate by Hydrogen Peroxide:  A Reinvestigation of Hypothiocyanite by Nuclear Magnetic Resonance and Optical Spectroscopy

Abstract

In an effort to reconcile conflicting reports regarding the spectra of the human defense factor hypothiocyanite (OSCN(-)), we have synthesized OSCN(-) by three methods and characterized the product spectroscopically. Method I is lactoperoxidase-catalyzed oxidation of SCN(-) by H(2)O(2) at pH 7. Method II is hydrolysis of (SCN)(2) at pH 13. Method III is oxidation of SCN(-) by OX(-) (X = Cl and Br) at pH 13. All three methods produced essentially the same initial UV, (13)C NMR, and (15)N NMR spectra. The UV spectrum reveals a lambda(max) of 376 nm, which is a previously unreported distinguishing feature. The (13)C NMR spectrum (delta = 127.8 ppm at pH 13 vs dioxane at 66.6 ppm) is comparable to those that have been previously reported for OSCN(-) as prepared by methods I and II (although in some cases different assignments have been made). However, the (15)N NMR spectrum we measure (delta = -80.6 ppm at pH 13 vs NO(3)(-) at 0 ppm) contrasts with previous reports. We conclude that all three methods produce the same species, and the spectra are now self-consistent with the formulation OSCN(-).

Comparative reactivity of the myeloperoxidase-derived oxidants HOCl and HOSCN with low-density lipoprotein (LDL): Implications for foam cell formation in atherosclerosis

“…However, the reactivity of the other major 38 MPO oxidant, hypothiocyanous acid (HOSCN) with LDL is poorly characterised, which is significant given 39 that thiocyanate is the favoured substrate for MPO. In this study, we comprehensively compare the 40 reactivity of HOCl and HOSCN with LDL, and show key differences in the profile of oxidative damage 41 observed. HOSCN selectively modifies Cys residues on apolipoprotein B100, and oxidises cholesteryl in inflammation and the production of a battery of oxidants [1].…”

Tryptophan oxidation in proteins exposed to thiocyanate-derived oxidants

“…Hydrogen peroxide [30% (v/v) solution; Sigma-Aldrich] was quantified by UV absorbance at 240 nm (e = 39.4 M À1 cm À1 ) [24]. Hypothiocyanite was quantified at 376 nm (e = 26.1 M À1 cm À1 ) [25].…”

Modification of IκBα by taurine bromamine inhibits tumor necrosis factor α-induced NF-κB activation

“…HOSCN was synthesized and quantifi ed as described previously [22]. The oxidation of SCN -by HOBr was achieved at pH 13 using turbulent mixing methods.…”