Deactivation of ferrylmyoglobin by vanillin as affected by vanillin binding to ß-lactoglobulin

TY - JOUR

T1 - Deactivation of ferrylmyoglobin by vanillin as affected by vanillin binding to ß-lactoglobulin

AU - Libardi, Silvia Helena

AU - borges, Julio C.

AU - Skibsted, Leif Horsfelt

AU - Cardoso, Daniel R.

PY - 2011/6/8

Y1 - 2011/6/8

N2 - Vanillin was found to be efficient as a deactivator of ferrylmyoglobin with a second-order rate constant of k2 = 57 ± 1 L mol -1 s-1 for reduction to metmyoglobin with ΔH ⧧ = 58.3 ± 0.3 kJ mol-1 and ΔS⧧ = -14 ± 1 J mol-1 K-1 in aqueous pH 7.4 solution at 25 °C. Binding to β-lactoglobulin (βLG) was found to affect the reactivity of vanillin at 25 °C only slightly to k2 = 48 ± 2 L mol-1 s-1 (ΔH⧧ = 68.4 ± 0.4 kJ mol-1 and ΔS⧧ = 17 ± 1 J mol-1 K-1) for deactivation of ferrylmyoglobin. Binding of vanillin to βLG was found to have a binding stoichiometry vanillin/βLG > 10 with KA = 6 × 102 L mol-1 and an apparent total ΔH° of approximately -38 kJ mol-1 and ΔS° = -55.4 ± 4 J mol-1 K -1 at 25 °C and ΔCp, obs = -1.02 kJ mol -1 K-1 indicative of increasing ordering in the complex, as determined by isothermal titration microcalorimetry. From tryptophan fluorescence quenching for βLG by vanillin, approximately one vanillin was found to bind to each βLG far stronger with KA = 5 × 104 L mol-1 and a ΔH° = -10.2 kJ mol -1 and ΔS° = 55 J mol-1 K-1 at 25 °C. The kinetic entropy/enthalpy compensation effect seen for vanillin reactivity by binding to βLG is concluded to relate to the weakly bound vanillin oriented through hydrogen bonds on the βLG surface with the phenolic group pointing toward the solvent, in effect making both ΔH ⧧ and ΔS⧧ more positive. The more strongly bound vanillin capable of tryptophan quenching in the βLG calyx seems less or nonreactive.

AB - Vanillin was found to be efficient as a deactivator of ferrylmyoglobin with a second-order rate constant of k2 = 57 ± 1 L mol -1 s-1 for reduction to metmyoglobin with ΔH ⧧ = 58.3 ± 0.3 kJ mol-1 and ΔS⧧ = -14 ± 1 J mol-1 K-1 in aqueous pH 7.4 solution at 25 °C. Binding to β-lactoglobulin (βLG) was found to affect the reactivity of vanillin at 25 °C only slightly to k2 = 48 ± 2 L mol-1 s-1 (ΔH⧧ = 68.4 ± 0.4 kJ mol-1 and ΔS⧧ = 17 ± 1 J mol-1 K-1) for deactivation of ferrylmyoglobin. Binding of vanillin to βLG was found to have a binding stoichiometry vanillin/βLG > 10 with KA = 6 × 102 L mol-1 and an apparent total ΔH° of approximately -38 kJ mol-1 and ΔS° = -55.4 ± 4 J mol-1 K -1 at 25 °C and ΔCp, obs = -1.02 kJ mol -1 K-1 indicative of increasing ordering in the complex, as determined by isothermal titration microcalorimetry. From tryptophan fluorescence quenching for βLG by vanillin, approximately one vanillin was found to bind to each βLG far stronger with KA = 5 × 104 L mol-1 and a ΔH° = -10.2 kJ mol -1 and ΔS° = 55 J mol-1 K-1 at 25 °C. The kinetic entropy/enthalpy compensation effect seen for vanillin reactivity by binding to βLG is concluded to relate to the weakly bound vanillin oriented through hydrogen bonds on the βLG surface with the phenolic group pointing toward the solvent, in effect making both ΔH ⧧ and ΔS⧧ more positive. The more strongly bound vanillin capable of tryptophan quenching in the βLG calyx seems less or nonreactive.

U2 - 10.1021/jf1047173

DO - 10.1021/jf1047173

M3 - Journal article

C2 - 21557578

SN - 0021-8561

VL - 59

SP - 6202

EP - 6208

JO - Journal of Agricultural and Food Chemistry

JF - Journal of Agricultural and Food Chemistry

IS - 11

ER -