Long-wavelength-absorbing forms of bacteriochlorophyll a in solutions of Triton X-100

Abstract

At least three forms of Triton X-100-solubilized bacteriochlorophyll a (BChI a) have been characterized by UV/ visible/near-IR absorption and CD spectra. One, absorbing at 770 nm, is similar to a monomeric solution in methanol. The two others have strongly red-shifted absorption peaks (860 nm and 930, 835 nm) and intense and complex CD bands in this region, indicative of strong interaction of at least two and three molecules of BChl a, respectively.Triton X-100 (II, m = 9 or 10) is next to dodecyldimethylamineoxide the most commonly used detergent for the isolation of bacterial reaction center and light-harvesting complexes.The understanding of bacterial photosynthesis has greatly advanced with the isolation and characterization of well-defined complexes of bacteriochlorophyll a (BChl a, I) with proteins ( (Fig. 2). The red shifts of these BCh1 a-protein complexes (as well as similar shifts in chlorophyll a-protein complexes) are as yet only partly understood and subject to much theoretical, spectroscopic, and synthetic work. They have been related to aggregation (5-14) or hydration (or both) (5,6,(12)(13)(14)(15), enolization of the chlorophyll groups (16)(17)(18)(19), point charges in their environment (20), and charge-transfer complexes (21). In particular, the primary donor P870 in BChl a-containing reaction centers has been suggested to be a "special pair" of BChl a, with their exact relationship still under discussion (22-27). IIWe noticed, during the isolation of reaction centers from Rhodospirillum rubrum G9 and Rhodopseudmownas spheroides R26 with Triton X-100, fractions that looked superficially like reaction centers contaminated with solubilized BChl a and bacteriopheophytin a. The 805-nm band was, however, small or even absent, and the 870-nm band was somewhat blue shifted and did not show any reversible bleaching. By systematic solubilization studies of BCh1 a with detergents, we have now shown that Triton X-100 induces strongly red-shifted absorption peaks in solubilized BChl a, with maxima around 830, 860, and 930 nm, and we here present our results on the BChl a species present in these solutions. EXPERIMENTALRs. rubrum G9 and Rp. spheroides R26 were grown in Hutner's medium (28) at 270C. BChl a was isolated by a modification of the method of Sato and Murata (29), which principally involves solvent extraction, precipitation of BChl a as a dioxane complex (30), and chromatography on DEAE-cellulose (29). The chromatography was alternatively also done on sugar columns (30). Triton X-100 was purchased from Serva (Heidelberg, Federal Republic of Germany) and used as received. All solvents were distilled or purified over alumina (Woelm, Eschwege, Federal Republic of Germany) prior to use. UV/visible/near-IR absorption spectra were recorded on a DMR 22 (Zeiss, Toberkochen, Federal Republic of Germany) spectrophotometer equipped for cross-illumination with suitable interference and cutoff filters. CD spectra were recorded with a dichrograph Mark V (Yvon-Jobin, Longjumeau, France) equipped w...

Structure-Function Relationships in Core Light-Harvesting Complexes (LHI) As Determined by Characterization of the Structural Subunit and by Reconstitution Experiments

“…tepidum (Jensen et al, 1964;Zuber and Brunisholz, 1991;Hawthornthwaite and Cogdell, 1991)). Even though the magnitude of the shifts are similar, one can not assume that all these wavelength shifts have the same structural origin (Gottstein and Scheer, 1983;Scherz and Parson, 1986;Brunisholz and Zuber, 1988;Pearlstein, 1988;Braun and Scherz, 1991;Thompson et al, 1991;Thompson and Fajer, 1992). Moreover, the circular dichroism (CD) spectra of LHI complexes show considerable variation among the photosynthetic bacteria (Bolt et al, 1981 a,b;Kramer et al, 1984;Cogdell and Scheer, 1985), indicating some differences in structure do exist.…”

Distribution and self-organization of photosynthetic pigments in micelles: implication for the assembly of light-harvesting complexes and reaction centers in the photosynthetic membrane.

“…A 3:1 (vol/vol) formamide/water solution (FW) was found to be conducive for the self-organization of various Chls and Bchls into large oligomers with spectral properties similar to those observed in vivo (25)(26)(27)(28)(29)(30)(31). Even though FW is hydrophilic, it imitates the in vivo pigment environment in two ways: (i) the formamide forms polymer chains that resemble the polypeptide backbone (32) and (ii) these polymer chains provide groups for hydrogen-bonding with the Bchl molecules.…”

“…The critical factors in the donor-acceptor type of dimerization are (i) the extent to which extraneous nucleophiles (e.g., H20) compete for coordination with the Mg and (ii) the availability of the keto group (18). Raman spectroscopy (22) (23) and Chls (24) and, recently, for various Bchls, bacteriopheophytins (Bphes), and Chls in aqueous solutions (3,(25)(26)(27)(28)(29)(30). Once the Chls and Bchls are attached to single polypeptides, their self-dimerization may affect the formation of protein networks in the LHCs and RCs.…”

“…ganic solvents containing traces of nucleophiles and (ii) a long wavelength-absorbing (L) form that resembles the particular pigment in vivo (3,(25)(26)(27)(28)(29)(30)(31). When the spectral properties of Bchl in the FW/Triton X-100 (TX-100) system was explored, the L form was found to be a dimer that resembled P-860 and the pigment centers in the LHC B850 (28,35).…”

An Overview of Chlorophylls and Bacteriochlorophylls: Biochemistry, Biophysics, Functions and Applications

“…As such, they are also integral to the stability of the systems. Chls show a remarkable potential for self-organization in both hydrophobic (Katz et al, 1978b;van Rossum et al, 2001) and hydrophilic media (Gottstein and Scheer, 1983;Katz et al, 1991;Scherz et al, 1991;Agostiano Fig. 4.…”