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Author Griffiths, J. A. ♦ El-Sayed, M. A. ♦ Capel, M.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword BIOLOGY AND MEDICINE, BASIC STUDIES ♦ CHEMISTRY ♦ EUROPIUM IONS ♦ CHEMICAL REACTIONS ♦ CHARGE DENSITY ♦ HOLMIUM IONS ♦ DYSPROSIUM IONS ♦ RHODOPSIN ♦ X-RAY DIFFRACTION ♦ BACTERIA ♦ PROTEINS ♦ CHEMICAL BONDS ♦ PH VALUE ♦ MATHEMATICAL MODELS ♦ COMPLEXES ♦ CRYSTAL STRUCTURE
Abstract The effect of the binding of trivalent lanthanide metal cations (Eu{sup 3+}, Ho{sup 3+}, and Dy{sup 3+}) on the hexagonal structure of bacteriorhodopsin (bR) is investigated at different pH using x-Ray diffraction to examine films made by slow evaporation of the corresponding regenerated bR. It is observed that the lanthanide-regenerated bR (at a ratio of 2:1 metal ion to bR) does not form a 2D structure isomorphous to that of native bR or Ca{sup 2+}-regenerated samples at low sample pH. The native bR hexagonal structure is recovered by titration of the sample with sodium hydroxide. The pH at which the hexagonal structure is recovered depends on the charge density of the lanthanide ion used for the regeneration. The higher the charge density of the ion, the higher pH at which an isomorphous lattice is formed. A model is proposed in which at normal or low pH a complex bidentate and monodentate type binding (which disrupts the lattice hexagonal structure) exists between a lanthanide ion, the O{sup -} of PO{sub 2}{sup -} groups, and/or the amino acid residues. At high pH, complexation with OH{sup -} takes place, which converts this binding to a simple monodentate type complex that leads to the recovery of the lattice structure. An equation is derived for the pH at which this conversion takes place. 48 refs., 4 figs.
ISSN 00223654
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-07-18
Publisher Place United States
Journal Journal of Physical Chemistry
Volume Number 100
Issue Number 29


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