Iron uptake by ferritin: NMR relaxometry studies at low iron loads

J. Vymazal, R. A. Brooks, J. W.M. Bulte, D. Gordon, P. Aisen

Research output: Contribution to journalArticle

Abstract

Twenty ferritin samples were prepared at pH 6.5 with average loadings of 0-89 Fe atoms per molecule. Nuclear magnetic relaxation times T1 and T2 were measured at 3°C, 23°C, and 37°C and at field strength from 0.025 to 1.5 T. The field dependence, temperature dependence, and approximate equality of T1 and T2 at low fields all suggest that nuclear magnetic relaxation in this range is caused primarily by solitary Fe3+ ions. The relaxivity (relaxation rate per mM ferritin) increases quickly with initial iron loading, reaches a peak at 13-14 Fe atoms per molecule, and then declines. This provides supportive evidence for the formation of antiferromagnetically- coupled clusters during early stages in iron loading; the failure to see a similar peak in an earlier study may be related to the nonphysiological pH that was used. Above 50 atoms per molecule, the relaxivity remains approximately constant, except that 1/T2 at high fields increases slightly, consistent with early core growth. The residual ionic relaxivity in this region is consistent with about three solitary Fe3+ ions remaining on the protein shell, indicating that spin cancellation is not complete. A similar value is obtained by extrapolating relaxation data at high loadings (up to 3000 Fe atoms per molecule), suggesting that these uncoupled spins persist on the protein shell even after an appreciable core has been built.

Original languageEnglish (US)
Pages (from-to)153-157
Number of pages5
JournalJournal of Inorganic Biochemistry
Volume71
Issue number3-4
DOIs
StatePublished - Sep 1 1998
Externally publishedYes

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Keywords

  • Ferritin
  • Iron
  • Relaxometry

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry

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