Polyethylene glycol promotes autoxidation of cytochrome c

• Published in: Biochimica et biophysica acta Vol. 1862; no. 6; pp. 1339 - 1349
• Main Authors: Sato, Wataru, Uchida, Takeshi, Saio, Tomohide, Ishimori, Koichiro
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.06.2018
• Subjects: absorption; autoxidation; cardiolipins; circular dichroism spectroscopy; Cytochrome c; Dehydration; denaturation; Electron transfer; fluorescence; Heme; hydrophobicity; oxygen; polyethylene glycol; redox potential; titration; Cytochrome c; PEG; NIR; Cyt b5; Heme; Electron transfer; Cyt c; FRET; Dehydration; WT; CcO
• ISSN: 0304-4165; 0006-3002; 1872-8006; 1872-8006
• DOI: 10.1016/j.bbagen.2018.03.010

Cytochrome c (Cyt c) was rapidly oxidized by molecular oxygen in the presence, but not absence of PEG. The redox potential of heme c was determined by the potentiometric titration to be +236 ± 3 mV in the absence of PEG, which was negatively shifted to +200 ± 4 mV in the presence of PEG. The underlying the rapid oxidation was explored by examining the structural changes in Cyt c in the presence of PEG using UV–visible absorption, circular dichroism, resonance Raman, and fluorescence spectroscopies. These spectroscopic analyses suggested that heme oxidation was induced by a modest tertiary structural change accompanied by a slight shift in the heme position (<1.0 Å) rather than by partial denaturation, as is observed in the presence of cardiolipin. The near-infrared spectra showed that PEG induced dehydration from Cyt c, which triggered heme displacement. The primary dehydration site was estimated to be around surface-exposed hydrophobic residues near the heme center: Ile81 and Val83. These findings and our previous studies, which showed that hydrated water molecules around Ile81 and Val83 are expelled when Cyt c forms a complex with CcO, proposed that dehydration of these residues is functionally significant to electron transfer from Cyt c to CcO. [Display omitted] •Reduced cytochrome c was rapidly oxidized in the presence of PEG.•Heme oxidation was induced by a tertiary structural change with a slight shift in the heme position.•PEG induces dehydration from Ile81 and Val83 of cytochrome c, which triggers the heme displacement.