bacteriochlorophylls and dodecyldimethylamine-oxide

The aim of this study is to reveal the interaction relationships between lauryl dimethylamine N-oxide (LDAO) and peripheral light-harvesting complex (LH2) as well as the influence of LDAO on structure and function of LH2. In the present work, the effects of LDAO on the conformation and release processes of bacteriochlorophyll (BChl) of LH2 when incubated under different temperature and pH in the presence and absence of LDAO were investigated by spectroscopy. The results indicated that (1) the presence of LDAO resulted in alterations in the conformation, alpha-helix content, and spectra of Tyr and B850 band of LH2 at room temperature and pH 8.0. Moreover, energy transfer efficiency of LH2 was enhanced markedly in the presence of LDAO. (2) At 60 degrees C, both the B800 and B850 band of LH2 were released and transited into free BChl at pH 8.0. However, the release rates of bacteriochlorophylls of B800 and B850 band from LH2 were slowed down and the release processes were changed when incubated in the presence of LDAO. Hence, the stability of LH2 was improved in the presence of LDAO. (3) The accelerated release processes of bacteriochlorophylls of B800 and B850 band of LH2 were induced to transform into bacteriopheophytin (BPhe) and free BChl by LDAO in strong acid and strong alkalic solution at room temperature. However, the kinetic patterns of the B800 and B850 band were remarkably different. The release and self-assemble processes of B850 in LH2 were observed in strong acid solution without LDAO. Therefore, the different release behaviors of B800 and B850 of LH2 are induced by LDAO under different extreme environmental conditions.

Topics: Bacterial Proteins; Bacteriochlorophylls; Dimethylamines; Energy Transfer; Kinetics; Light-Harvesting Protein Complexes; Pheophytins; Protein Structure, Secondary; Rhodobacter

We demonstrate that the B800-830 spectral form of the B800-850 peripheral light-harvesting complex of Rhodobacter sulphidophilus, which is formed at low ionic strengths in the presence of the zwitterionic detergent LDAO, results from a local modification of the bacteriochlorophyll binding site and not the dissociation of the complex. This perturbation does not result in significant changes to the interactions between the pigments as studied by circular dichroism or fluorescence spectroscopy; however, modifications in the pigment binding sites are inferred from changes in the preresonance Raman spectrum. Specifically, an alteration of the hydrogen bonding of the 2-acetyl group of at least one of the bacteriochlorophyll groups that make up the 850 nm absorbing pair is observed. This implies an alteration in the conformation of the C-terminal domain of the alpha-polypeptide, in which are located the two tyrosyl residues that are believed to act as H-bond donors to these groups, induced by the protein-bound detergent in the absence of bound cations. We suggest that the ability of this complex to form an 800-830 complex is linked to the presence of an aspartyl residue immediately upstream of the tyrosyl residues. This study therefore provides a further illustration of the importance of hydrogen bonds to the 2-acetyl group of the bacteriochlorophyll in the determination of its spectral properties; furthermore, we provide a description of a conformational change that is able to modulate chromophore binding in these complexes.

Topics: Bacteriochlorophylls; Binding Sites; Chromatography, Gel; Circular Dichroism; Dimethylamines; Hydrogen Bonding; Light-Harvesting Protein Complexes; Mutagenesis, Site-Directed; Osmolar Concentration; Photosynthetic Reaction Center Complex Proteins; Protein Conformation; Rhodobacter; Spectrometry, Fluorescence; Spectrophotometry; Spectrum Analysis, Raman

Topics: Bacterial Proteins; Bacteriochlorophylls; Dimethylamines; Iron; Light-Harvesting Protein Complexes; Mathematics; Molecular Weight; Pheophytins; Phospholipids; Photosynthetic Reaction Center Complex Proteins; Protein Binding; Protein Conformation; Rhodobacter sphaeroides; Ubiquinone

When reaction center particles from Rhodopseudomonas spheroides strain R26 are illuminated and then extracted with methanol, about one-third of the extracted bacteriochlorophyll slowly becomes oxidized, The oxidation does not occur under anaerobic conditions or in the absence of the detergent lauryldimethylamine oxide. Alkaline conditions also prevent the reaction. A dark interval between illumination and extraction delays the onset of bacteriochlorophyll oxidation in a predictable way. These results are consistent with the hypothesis that illumination generates a reaction initiator which is fairly stable in methanol but decays with a half-life of about 4.5 min in reaction center particles after illumination ceases.

Topics: Bacteriochlorophylls; Darkness; Detergents; Dimethylamines; Hydrogen-Ion Concentration; Light; Oxidation-Reduction; Oxygen; Photosynthetic Reaction Center Complex Proteins; Rhodopseudomonas