%0 Journal Article %J Proceedings of the National Academy of Sciences of the United States of America %D 1996 %T Detection of a Yb3+ binding site in regenerated bacteriorhodopsin that is coordinated with the protein and phospholipid head groups. %A Roselli, Cecile %A Boussac, A %A Mattioli, T A %A Griffiths, Jennifer A. %A El-Sayed, Mostafa A %K Bacteriorhodopsins %K Binding Sites %K Metals, Rare Earth %K Phospholipids %K Retinaldehyde %K Spectroscopy, Near-Infrared %X Near infrared Yb3+ vibronic sideband spectroscopy was used to characterize specific lanthanide binding sites in bacteriorhodopsin (bR) and retinal free bacteriorhodopsin (bO). The VSB spectra for deionized bO regenerated with a ratio of 1:1 and 2:1 ion to bO are identical. Application of a two-dimensional anti-correlation technique suggests that only a single Yb3+ site is observed. The Yb3+ binding site in bO is observed to consist of PO2- groups and carboxylic acid groups, both of which are bound in a bidentate manner. An additional contribution most likely arising from a phenolic group is also observed. This implies that the ligands for the observed single binding site are the lipid head groups and amino acid residues. The vibronic sidebands of Yb3+ in deionized bR regenerated at a ratio of 2:1 ion to bR are essentially identical to those in bO. The other high-affinity binding site is thus either not evident or its fluorescence is quenched. A discussion is given on the difference in binding of Ca2+ (or Mg2+) and lanthanides in phospholipid membrane proteins. %B Proceedings of the National Academy of Sciences of the United States of America %V 93 %P 14333-7 %8 1996 Dec 10 %G eng %N 25 %1 http://www.ncbi.nlm.nih.gov/pubmed/8962051?dopt=Abstract