Outer-sphere oxidation of Fe(II) in nitrosylmyoglobin by ferricyanide

TY - JOUR

T1 - Outer-sphere oxidation of Fe(II) in nitrosylmyoglobin by ferricyanide

AU - Møller, Jens K.S.

AU - Skibsted, Leif Horsfelt

PY - 2014/8

Y1 - 2014/8

N2 - Nitrosylmyoglobin, MbFe(II)NO, was found to be oxidized by [Fe(CN) 6]3- and HClO/ClO-, but not by the semistable radical nitrosodisulfonate (anion of Frémy's salt) or NO2 - at ambient temperature in aqueous solution with pH 7.0. The oxidation by HClO/ClO- was significantly faster than that by [Fe(CN)6]3-. With excess [Fe(CN)6] 3-, MbFe(II)NO was oxidized to metmyoglobin, MbFe(III), in a second-order reaction with k 2 = 1.67 ± 0.10 M-1 s-1 at 288 K without detectable intermediates as determined by stopped-flow spectroscopy. The activation parameters were ΔH ‡ = 43 ± 2 kJ mol-1 and ΔS ‡ = -93 ± 9 J-1 K-1 mol -1. Outer-sphere electron-transfer to [Fe(CN)6] 3- was assigned as rate determining rather than NO dissociation from iron(II) followed by electron transfer. Outer-sphere electron transfer from MbFe(II)NO to certain moderate oxidizing agents may thus have a role in labilizing NO association slowly through oxidation of iron(II) to iron(III). In contrast, hypochlorite oxidizes MbFe(II)NO much faster in a complex sequence of processes involving a rate-determining second-order (unidentified) reaction with k 2 = 2.6 ± 0.3 × 103 M-1 s -1 at 288 K and possibly involving protein degradation.

AB - Nitrosylmyoglobin, MbFe(II)NO, was found to be oxidized by [Fe(CN) 6]3- and HClO/ClO-, but not by the semistable radical nitrosodisulfonate (anion of Frémy's salt) or NO2 - at ambient temperature in aqueous solution with pH 7.0. The oxidation by HClO/ClO- was significantly faster than that by [Fe(CN)6]3-. With excess [Fe(CN)6] 3-, MbFe(II)NO was oxidized to metmyoglobin, MbFe(III), in a second-order reaction with k 2 = 1.67 ± 0.10 M-1 s-1 at 288 K without detectable intermediates as determined by stopped-flow spectroscopy. The activation parameters were ΔH ‡ = 43 ± 2 kJ mol-1 and ΔS ‡ = -93 ± 9 J-1 K-1 mol -1. Outer-sphere electron-transfer to [Fe(CN)6] 3- was assigned as rate determining rather than NO dissociation from iron(II) followed by electron transfer. Outer-sphere electron transfer from MbFe(II)NO to certain moderate oxidizing agents may thus have a role in labilizing NO association slowly through oxidation of iron(II) to iron(III). In contrast, hypochlorite oxidizes MbFe(II)NO much faster in a complex sequence of processes involving a rate-determining second-order (unidentified) reaction with k 2 = 2.6 ± 0.3 × 103 M-1 s -1 at 288 K and possibly involving protein degradation.

U2 - 10.1007/s00775-014-1112-y

DO - 10.1007/s00775-014-1112-y

M3 - Journal article

C2 - 24522282

SN - 0949-8257

VL - 19

SP - 805

EP - 812

JO - Journal of Biological Inorganic Chemistry

JF - Journal of Biological Inorganic Chemistry

IS - 6

ER -