Biophysical Journal 71: 1587-1595 (1996)
© 1996 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Yang, X Articles by Chasteen, N D Search for Related Content PubMed PubMed Citation Articles by Yang, X Articles by Chasteen, N D

Molecular diffusion into horse spleen ferritin: a nitroxide radical spin probe study.

Department of Chemistry, University of New Hampshire, Durham 03824, USA.

ABSTRACT

Electron paramagnetic resonance spectroscopy and gel permeation chromatography were employed to study the molecular diffusion of a number of small nitroxide spin probes (approximately 7-9 A diameter) into the central cavity of the iron-storage protein ferritin. Charge and polarity of these radicals play a critical role in the diffusion process. The negatively charged radical 4-carboxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4-carboxy-TEMPO) does not penetrate the cavity whereas the positively charged 4-amino-TEMPO and 3-(aminomethyl)-proxyl radical and polar 4-hydroxy-TEMPO radical do. Unlike the others, the apolar TEMPO radical does not enter the cavity but instead binds to ferritin, presumably at a hydrophobic region of the protein. The kinetic data indicate that diffusion is not purely passive, the driving force coming not only from the concentration gradient between the inside and outside of the protein but also from charge interactions between the diffusant and the protein. A model for diffusion is derived that describes the observed kinetics. First-order half-lives for diffusion into the protein of 21-26 min are observed, suggesting that reductant molecules with diameters considerably larger than approximately 9 A would probably enter the protein cavity too slowly to mobilize iron efficiently by direct interaction with the mineral core.

This article has been cited by other articles:

				F. Bou-Abdallah, A. C. Lewin, N. E. Le Brun, G. R. Moore, and N. D. Chasteen Iron Detoxification Properties of Escherichia coli Bacterioferritin. ATTENUATION OF OXYRADICAL CHEMISTRY J. Biol. Chem., September 27, 2002; 277(40): 37064 - 37069. [Abstract] [Full Text] [PDF]

				C. M. Barnes, E. C. Theil, and K. N. Raymond Iron uptake in ferritin is blocked by binding of [Cr(TREN)(H2O)(OH)]2+, a slow dissociating model for [Fe(H2O)6]2+ PNAS, April 16, 2002; 99(8): 5195 - 5200. [Abstract] [Full Text] [PDF]