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<p>In the reaction of aquacobalamin (aquaCbl) with chlorite, a stable species is detected and assigned as a Co(III)–chlorite complex, Co(III)–OClO<sup>−</sup>. Its UV–Vis spectrum is almost identical to that of aquaCbl, except for some minor differences at ~ 430&#xa0;nm; cyanide can eliminate and prevent these changes. The <sup>1</sup>H-NMR spectra reveal strong influences of chlorite on the B2 and B4 protons of the cobalt-bound dimethyl benzimidazole ligand. Together, the UV–Vis and NMR titrations suggest a Kd of 10&#xa0;mM or higher for chlorite on Cbl. Resonance Raman spectra reveal minor changes in the spectrum of aquaCbl to chlorite—as well as a disappearance of the free chlorite signals, consistent with Cbl–chlorite complex formation. Corroboration for these interpretations is also offered from mass spectrometry and DFT calculations. This Co(III)–OClO<sup>−</sup> complex would be a stable analogue of the first reaction intermediate in the catalytic cycle of chlorite dismutase, or in the reaction of chlorite with a number of other heme proteins. The differences in reactivity between Co(III) cobalamin and Fe(III) heme towards chlorite are analyzed and rationalized, leading to a reconciliation of experimental and computational data for the latter.</p>

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The chlorite adduct of aquacobalamin: contrast with chlorite dismutase

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年2月9日

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  • Maria Lehene,
  • Cezara Zagrean-Tuza,
  • Stefania D. Iancu,
  • Sergiu-Raul Cosma,
  • Adrian M. V. Brânzanic,
  • Radu Silaghi-Dumitrescu,
  • Bianca Stoean

摘要

In the reaction of aquacobalamin (aquaCbl) with chlorite, a stable species is detected and assigned as a Co(III)–chlorite complex, Co(III)–OClO−. Its UV–Vis spectrum is almost identical to that of aquaCbl, except for some minor differences at ~ 430 nm; cyanide can eliminate and prevent these changes. The 1H-NMR spectra reveal strong influences of chlorite on the B2 and B4 protons of the cobalt-bound dimethyl benzimidazole ligand. Together, the UV–Vis and NMR titrations suggest a Kd of 10 mM or higher for chlorite on Cbl. Resonance Raman spectra reveal minor changes in the spectrum of aquaCbl to chlorite—as well as a disappearance of the free chlorite signals, consistent with Cbl–chlorite complex formation. Corroboration for these interpretations is also offered from mass spectrometry and DFT calculations. This Co(III)–OClO− complex would be a stable analogue of the first reaction intermediate in the catalytic cycle of chlorite dismutase, or in the reaction of chlorite with a number of other heme proteins. The differences in reactivity between Co(III) cobalamin and Fe(III) heme towards chlorite are analyzed and rationalized, leading to a reconciliation of experimental and computational data for the latter.