Primary electron transfer kinetics in bacterial reaction centers with modified bacteriochlorophylls at the monomeric sites BA,B.
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The primary electron transfer has been investigated by femtosecond time-resolved absorption spectroscopy in two chemically modified reaction centers (RC) of Rhodobacter sphaeroides, in which the monomeric bacteriochlorophylls BA and BB have both been exchanged by 13(2)-hydroxybacteriochlorophyll a or [3-vinyl]-13(2)-hydroxybacteriochlorophyll a. The kinetics of the primary electron transfer are not influenced by the 13(2)-hydroxy modification. In RCs containing [3-vinyl]-13(2)-hydroxybacteriochlorophyll a the primary rate is reduced by a factor of 10. (+info)
The stereospecific interaction between chlorophylls and chlorophyllase. Possible implication for chlorophyll biosynthesis and degradation.
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Chlorophyllase-catalyzed hydrolysis and esterification of chlorophylls, bacteriochlorophylls, and their free acids, respectively, depend on the configuration around the C-13(2) atom of the corresponding substrate. The data suggest that the enzyme interacts preferentially with compounds having the isocyclic carbomethoxy and the C-17 propionic residues facing opposite sides of the porphyrin macrocycle. The relevance of this observation to chlorophyll biosynthesis and degradation in vivo is briefly discussed. (+info)
Characterization of Chlorobium tepidum chlorosomes: a calculation of bacteriochlorophyll c per chlorosome and oligomer modeling.
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The bacteriochlorophyll (Bchl) c content and organization was determined for Chlorobium (Cb.) tepidum chlorosomes, the light-harvesting complexes from green photosynthetic bacteria, using fluorescence correlation spectroscopy and atomic force microscopy. Single-chlorosome fluorescence data was analyzed in terms of the correlation of the fluorescence intensity with time. Using this technique, known as fluorescence correlation spectroscopy, chlorosomes were shown to have a hydrodynamic radius (Rh) of 25 +/- 3.2 nm. This technique was also used to determine the concentration of chlorosomes in a sample, and pigment extraction and quantitation was used to determine the molar concentration of Bchl c present. From these data, a number of approximately 215,000 +/- 80,000 Bchl c per chlorosome was determined. Homogeneity of the sample was further characterized by dynamic light scattering, giving a single population of particles with a hydrodynamic radius of 26.8 +/- 3.7 nm in the sample. Tapping-mode atomic force microscopy (TMAFM) was used to determine the x,y,z dimensions of chlorosomes present in the sample. The results of the TMAFM studies indicated that the average chlorosome dimensions for Cb. tepidum was 174 +/- 8.3 x 91.4 +/- 7.7 x 10.9 +/- 2.71 nm and an overall average volume 90,800 nm(3) for the chlorosomes was determined. The data collected from these experiments as well as a model for Bchl c aggregate dimensions was used to determine possible arrangements of Bchl c oligomers in the chlorosomes. The results obtained in this study have significant implications on chlorosome structure and architecture, and will allow a more thorough investigation of the energetics of photosynthetic light harvesting in green bacteria. (+info)
Identification of intramembrane hydrogen bonding between 13(1) keto group of bacteriochlorophyll and serine residue alpha27 in the LH2 light-harvesting complex.
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Intramembrane hydrogen bonding and its effect on the structural integrity of purple bacterial light-harvesting complex 2, LH2, have been assessed in the native membrane environment. A novel hydrogen bond has been identified by Raman resonance spectroscopy between a serine residue of the membrane-spanning region of LH2 alpha-subunit, and the C-13(1) keto carbonyl of bacteriochlorophyll (BChl) B850 bound to the beta-subunit. Replacement of the serine by alanine disrupts this strong hydrogen bond, but this neither alters the strongly red-shifted absorption nor the structural arrangement of the BChls, as judged from circular dichroism. It also decreases only slightly the thermal stability of the mutated LH2 in the native membrane environment. The possibility is discussed that weak H-bonding between the C-13(1) keto carbonyl and a methyl hydrogen of the alanine replacing serine(-4) or the imidazole group of the nearby histidine maintains structural integrity in this very stable bacterial light-harvesting complex. A more widespread occurrence of H-bonding to C-13(1) not only in BChl, but also in chlorophyll proteins, is indicated by a theoretical analysis of chlorophyll/polypeptide contacts at <3.5 A in the high-resolution structure of Photosystem I. Nearly half of the 96 chlorophylls have aa residues suitable as hydrogen bond donors to their keto groups. (+info)
Exciton theory for supramolecular chlorosomal aggregates: 1. Aggregate size dependence of the linear spectra.
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The interior of chlorosomes of green bacteria forms an unusual antenna system organized without proteins. The steady-spectra (absorption, circular dichroism, and linear dichroism) have been modeled using the Frenkel Hamiltonian for the large tubular aggregates of bacteriochlorophylls with geometries corresponding to those proposed for Chloroflexus aurantiacus and Chlorobium tepidum chlorosomes. For the Cf. aurantiacus aggregates we apply a structure used previously (V. I. Prokhorenko., D. B. Steensgaard, and A. R. Holzwarth, Biophys: J. 2000, 79:2105-2120), whereas for the Cb. tepidum aggregates a new extended model of double-tube aggregates, based on recently published solid-state nuclear magnetic resonance studies (B.-J. van Rossum, B. Y. van Duhl, D. B. Steensgaard, T. S. Balaban, A. R. Holzwarth, K. Schaffner, and H. J. M. de Groot, Biochemistry 2001, 40:1587-1595), is developed. We find that the circular dichroism spectra depend strongly on the aggregate length for both types of chlorosomes. Their shape changes from "type-II" (negative at short wavelengths to positive at long wavelengths) to the "mixed-type" (negative-positive-negative) in the nomenclature proposed in K. Griebenow, A. R. Holzwarth, F. van Mourik, and R. van Grondelle, Biochim: Biophys. Acta 1991, 1058:194-202, for an aggregate length of 30-40 bacteriochlorophyll molecules per stack. This "size effect" on the circular dichroism spectra is caused by appearance of macroscopic chirality due to circular distribution of the transition dipole moment of the monomers. We visualize these distributions, and also the corresponding Frenkel excitons, using a novel presentation technique. The observed size effects provide a key to explain many previously puzzling and seemingly contradictory experimental data in the literature on the circular and linear dichroism spectra of seemingly identical types of chlorosomes. (+info)
Selectivity of the photosensitiser Tookad for photodynamic therapy evaluated in the Syrian golden hamster cheek pouch tumour model.
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The response to photodynamic therapy (PDT) with the photosensitiser (PS) Tookad was measured in the Syrian hamster cheek pouch model on normal mucosae and chemically induced squamous cell carcinoma. This PS is a palladium-bacteriopheophorbide presenting absorption peaks at 538 and 762 nm. The light dose, drug dose and drug injection-light irradiation times (DLI), ranging between 100 and 300 J cm(-2), 1-5 mg kg(-1) and 10-240 min respectively, were varied and the response to PDT was analysed by staging the macroscopic response and by the histological examination of the sections of the irradiated cheek pouch. A fast time decay of the tissular response with drug dose of 1-5 mg kg(-1) was observed for DLI ranging from 10 to 240 min and for light doses of 100-300 J cm(-2) delivered at a light dose rate of 150 mW cm(-2). A significantly higher level of tissular response was observed for squamous cell carcinoma compared to normal tissue. Nevertheless, the threshold level of the drug-light dose for a detectable response was not significantly different in the tumoral vs normal tissue. The highest response at the shortest DLIs and the absence of measurable response at DLI larger than 240 min at light dose of 300 J cm(-2) and drug dose of 5 mg kg(-1) reveals the predominantly vascular effect of Tookad. This observation suggests that Tookad could be effective in PDT of vascularised lesions. (+info)
Combined hyperthermia and chlorophyll-based photodynamic therapy: tumour growth and metabolic microenvironment.
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The effects of combined and simultaneously applied localised 43 degrees C hyperthermia (HT) and an antivascular bacteriochlorophyll-serine-based photodynamic therapy (Bchl-ser-PDT) on tumour growth and several microenvironmental parameters were examined. Rats bearing DS-sarcomas were allocated to treatment groups: (i) sham-treatment (control), (ii) Bchl-ser-PDT (20 mg kg(-1) i.v.), (iii) localised HT, (iv) Bchl-ser-PDT+HT. The light source used was an infrared-A irradiator, which, by use of appropriate filters, delivered the different ranges of wavelengths required. Following treatment, tumour volume was monitored. The greatest tumour growth inhibition was seen with Bchl-ser-PDT+HT, and subsequent experiments identified the pathophysiological basis for this effect. Red blood cell flux in tumour microvessels declined rapidly upon Bchl-ser-PDT+HT, reaching approximately 10% of initial values by the end of treatment. Similarly, tumour oxygenation worsened, reaching almost anoxic levels by the end of the treatment period. Assessment of metabolic parameters showed a pronounced increase in lactate levels and a decrease in ATP concentrations after combined treatment. The results presented suggest that vascular collapse and flow stasis resulting in a deterioration of tumour oxygenation and a switch from oxidative to glycolytic glucose turnover are key elements in the tumour eradication seen with this novel approach in which an antivascular PDT and HT are combined and simultaneously applied. (+info)
Presence of exclusively bacteriochlorophyll-c containing substrain in the culture of green sulfur photosynthetic bacterium Chlorobium vibrioforme strain NCIB 8327 producing bacteriochlorophyll-d.
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The light-dependent composition change of light harvesting bacteriochlorophyll(BChl)s in the present culture of a green sulfur photosynthetic bacterium Chlorobium (Chl.) vibrioforme f. sp. thiosulfatophilum strain NCIB 8327 was investigated by visible absorption spectroscopy and HPLC analyses. When the culture was repeatedly grown in liquid media under a low light condition, both the Soret and Qy absorption bands of the in vivo spectrum were shifted to longer wavelengths. Analysis of the extracted pigments by HPLC revealed that the ratio of the amount of BChl-c to that of BChl-d molecules gradually increased during repeated cultivation. In contrast, when the culture grown under a low light intensity was transferred to a high light condition and continued to be grown, the absorption bands were shifted to shorter wavelengths and the ratio of BChls-c/d decreased finally to the almost original value. Colonies were prepared on solid agar media from the liquid culture containing both BChls-c and d, which was grown under a low light intensity. Each colony obtained was found to contain either BChl-c or d, but not both of them. Two types of cells isolated in this study were derived from the same clone, judged from their genetic analyses. The variation of pigment composition in our liquid culture observed here could be ascribed to the difference of growth rates between two substrains containing BChl-c and BChl-d, respectively, depending on light conditions. (+info)