Comparative studies on manganese-based SOD mimetics, including the phosphate effect, by using global spectral analysis

Stopped-flow measurements have been successfully combined with time-resolved UV/vis spectroscopy and global spectral analysis of superoxide decay for the comparative study of catalytic activity of putative manganese SOD (superoxide dismutase) mimetics known in the literature. The SOD activity of the studied complexes decreases in the following order: a) M40403 > Mn(III)TM-4-PyP5 + > Mn(II)pyane > > EUK-113 at pH 7.4 (M40403 = ([manganese(II)dichlorido{(4R,9R,14R,19R)-3,10,13,20,26-pentaazatetracyclo[20.3.1.0.4,9014,19]hexacosa-1(26),-22(23),24-triene}], Mn(III)TM-4-PyP5 + = Mn(III)meso-tetrakis(N-methylpyridinium-4-yl)porphyrin, Mn(II)Pyane = Mn(II)trans-2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]-octadeca-1(18),14,16-triene, EUK-113 = [manganese(III)acetato(6,6′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenolate)]) in Hepes buffer (Hepes = 4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid), b) Mn(III)TM-4-PyP5 + > M40403 ≅ Mn(II)pyane > > EUK-113 at pH 8.1 in Hepes buffer and c) Mn(III)TM-4-PyP5 + ≅ Mn(II)pyane > MnCl2 > M40403 ≅ EUK-113 at pH 7.4 in phosphate buffer. MnCl2 in Hepes, Mn(III)TSPP3 −, Mn(III)TBAP3 −, Mn(III)acetate, Mn(II)lactate and Mn(II)EDTA do not exhibit SOD activity (Mn(III)TSPP3 − = Mn(III)mesotetrakis(benzoic acid)porphyrin, Mn(III)TBAP3 − = Mn(III)mesotetrakis(4-sulfonatophenyl)porphyrin). MnCl2 possess SOD activity that is comparable with those of other mimetics in the presence of phosphate. Our results demonstrate that phosphate anions, independent of ionic strength effect, influence the activity of manganese SOD mimetics, which is crucial for understanding and comparing their biological activity.

Applying time-resolved UV/vis spectroscopy and global spectra analysis of superoxide decay, we performed comparative studies of important representatives of putative Mn-SOD mimetics (MnSODm). We find that phosphate ions, independent of the ionic strength, strongly influence the SOD activity of MnSODm, questioning the nature of the active species under physiological conditions.Figure optionsDownload as PowerPoint slideHighlights
► Reliable direct measurements of SOD activity by time-resolved UV/Vis spectroscopy.
► Use of global spectra analysis for estimation of SOD activity.
► Comparative studies of manganese SOD mimetics.
► Influence of phosphate medium on activity of Mn-SOD mimetics.
► SOD activity of MnCl2 is comparable to other Mn-SOD mimetics in phosphate buffer.