X‐ray absorption studies on bacteriorhodopsin

Abstract

Extended X-ray absorption (EXAFS) measurements of iron-substituted bacteriorhodopsin revealed for the light-adapted state (bR LA) a homogeneous distribution of the first-shell ligands of iron. In Contrary to this result, the dark-adapted (bR DA) and the M-state (bR M) display significant heterogeneity at the iron site with bR DA intermediate between bR M and bR LA in average distance. These data provide direct evidence of structural changes at the membrane associated with photocycle changes at the cation-binding site.

An extended x-ray absorption fine structure study of the high-affinity cation-binding site in the purple membrane

“…Our results clearly show that the first coordination shell for Mn2+ is formed exclusively by oxygen atoms in a (distorted) octahedral coordination; similar results we] tained by using Fe3+ (Engelhard et al, 1987). Howevc composition of the second coordination shell constiti more open question.…”

“…Although a previous EXAFS study on Fe3+-substituted BR showed the presence of a relatively intense peak corresponding to the second shell at 2.4/2.8 A in the Fourier-transformed plot (Engelhard et al, 1987), it has to be pointed out that this work was performed under different conditions, namely, i) very low temperature was used, which can a priori enhance the intensities observed in the FT plot, ii) a trivalent cation was used, which impairs the photocycle by an order of magnitude (Engelhard et al, 1990). This last observation suggests that Mn2+ and Fe3+ are in fact occupying different binding sites.…”

“…Two samples, Mn2+ in solution and the complex BR-Mn2+ (1:1 molar ratio), have been compared. In a previous work, Engelhard et al (1987) carried out EXAFS measurements of Fe3+-substituted BR, which provided an evidence of structural changes at the binding site, associated with changes in the photocycle.…”

Studies of cation binding in ZnCl2-regenerated bacteriorhodopsin by x-ray absorption fine structures: effects of removing water molecules and adding Cl- ions

“…Studies on Pb2+-regenerated bR films (Katre et al, 1986;Mitra and Stroud, 1990) indicate that up to four distinct binding sites are located on the a-helices of the protein. In another study (Englehard et al, 1987), XAFS of Fe3+ was carried out to investigate the binding environment of the Fe3+ cations in bR. The results (Englehard et al, 1987) suggest an octahedral geometry for the metal ions with 5.8 ± 1.5 ligands.…”

Integrated optical application of bacteriorhodopsin

“…Structure and function of proteins can be studied by a lot of spectroscopic methods, ranging from X-rays to terahertz frequencies [39][40][41][42][43][44][45]. In this work, we deal only with spectroscopic properties in the visible region.…”