Chloramine-T-Mediated Oxidation of Benzylic Alcohols Using Indium(III) Triflate

Nakahara, Kazuhide; Kitazawa, Chie; Mineno, Tomoko

doi:10.1248/cpb.c17-00061

Cited by 1 publication

(1 citation statement)

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“…The role of metal catalysis in CT-induced oxidation of small organic substrates has been examined previously, e.g., for Os(VIII) oxide and In(III) triflate. , However, there seems to be no prior work related to the reactivity of CT in the presence of Fe or heme. We consider it most likely that the heme-catalyzed Lys oxidation seen here involves OCl – .…”

Section: Discussionmentioning

confidence: 99%

Delineating Heme-Mediated versus Direct Protein Oxidation in Peroxidase-Activated Cytochrome c by Top-Down Mass Spectrometry

2020

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Oxidation of key residues in cytochrome c (cyt c) by chloramine T (CT) converts the protein from an electron transporter to a peroxidase. This peroxidase-activated state represents an important model system for exploring the early steps of apoptosis. CT-induced transformations include oxidation of the distal heme ligand Met80 (MetO, +16 Da) and carbonylation (LysCHO, −1 Da) in the range of Lys53/55/72/ 73. Remarkably, the 15 remaining Lys residues in cyt c are not susceptible to carbonylation. The cause of this unusual selectivity is unknown. Here we applied top-down mass spectrometry (MS) to examine whether CT-induced oxidation is catalyzed by heme. To this end, we compared the behavior of cyt c with (holo-cyt c) and without heme (apo SS -cyt c). CT caused MetO formation at Met80 for both holo-and apo SS -cyt c, implying that this transformation can proceed independently of heme. The aldehyde-specific label Girard's reagent T (GRT) reacted with oxidized holo-cyt c, consistent with the presence of several LysCHO. In contrast, oxidized apo-cyt c did not react with GRT, revealing that LysCHO forms only in the presence of heme. The heme dependence of LysCHO formation was further confirmed using microperoxidase-11 (MP11). CT exposure of apo SS -cyt c in the presence of MP11 caused extensive nonselective LysCHO formation. Our results imply that the selectivity of LysCHO formation at Lys53/55/72/73 in holocyt c is caused by the spatial proximity of these sites to the reactive (distal) heme face. Overall, this work highlights the utility of topdown MS for unravelling complex oxidative modifications.

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Section: Discussionmentioning

confidence: 99%