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USE OF THE FLUORESCENT LANTHANIDE Tb 3+ AS A PROBE FOR CATION‐BINDING SITES ASSOCIATED WITH ISOLATED CHLOROPLAST THYLAKOID MEMBRANES
Author(s) -
Mills John D.,
Hind Geoffrey
Publication year - 1978
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1978.tb06931.x
Subject(s) - thylakoid , fluorescence , chemistry , chloroplast , membrane , lanthanide , binding site , ion , photochemistry , biophysics , crystallography , biochemistry , biology , organic chemistry , quantum mechanics , physics , gene
Abstract— The fluorescent properties of the rare‐earth ion, Tb 3+ have been utilized to probe the nature of cation‐binding sites associated with thylakoid membranes. At low concentrations (< 100μ M ), Tb 3+ was observed to inhibit the increase in chlorophyll a fluorescence normally seen on adding 5 m M MgCl 2 (or 100 m M NaCl) to isolated, broken chloroplasts. We also observed under these conditions, the appearance of a new band around 280 nm in the excitation spectrum of Tb 3+ ion fluorescence. However, similar changes in Tb 3+ fluorescence could be observed in the presence of a membrane‐free preparation of chloroplast coupling factor protein (CF 1 ). From this and other results it is concluded that changes in Tb 3+ fluorescence reflect an association of the ion with CF 1 followed by intermolecular transfer of excitation energy from protein ligands (possibly un‐ionized tyrosine residues) to the lanthanide. The interaction of Tb 3+ with sites which control chlorophyll a fluorescence does not seem to modify Tb 3+ fluorescence, suggesting that in this case, simple membrane‐bound ligands such as carboxyl or phosphate groups are involved.