Hidenori Hayashi

Factors controlling the efficiency of energy transfer from carotenoids to bacteriochlorophyll in purple photosynthetic bacteria

Abstract Efficiencies of energy transfer from carotenoids to bacteriochlorophyll in purple photosynthetic bacteria have been studied with chromatophores, isolated pigment-protein complexes, and pigment-protein complexes reconstituted with a variety of carotenoids. Based on the efficiencies of energy transfer and the chemical structure of major carotenoids, photosynthetic bacteria used in this study are classified into two groups. (1) Rhodobacter sphaeroides, Rhodobacter capsulatus, and Rhodocyclus gelatinosus show relatively high efficiencies (>70%) and contain spheroidene-series carotenoids which have nine or ten conjugated C=C bonds. (2) Rhodopseudomonas palustris, Rhodospirillum rubrum, and Chromatium vinosum show relatively low efficiencies (

Resonance Raman studies of the conformations of all-Trans carotenoids in light-harvesting systems of photosynthetic bacteria

Abstract Comparison of the resonance Raman spectra of carotenoids in vivo and in vitro has revealed that in some species of photosynthetic bacteria the major fraction of carotenoids associated with the light-harvesting systems has forms distorted (twisted) from the planar all-trans conformation. These distorted forms are kept in isolated and purified light-harvesting bacteriochlorophyll-protein complexes.

Bacteriochlorophyll-protein complexes of aerobic bacteria, Erythrobacter longus and Erythrobacter species OCh 114

Bacteriochlorophyll(Bchl)-protein complexes were isolated from obligate aerobic bacteria, Erythrobacter longus and Erythrobacter species OCh 114. The apparent molecular weights, absorption spectra and polypeptide compositions of the light-harvesting complexes were, in general, similar to those of the light-harvesting Bchl-protein complexes of purple photosynthetic bacteria. The reaction center complexes of these bacteria also showed similar properties to those of the purple bacteria except for slightly altered polypeptides. However, the following characteristic features of the light-harvesting systems were found in these aerobic bacteria. Major carotenoids were not bound to the Bchl-protein complex in E. longus. In Erythrobacter sp. OCh 114, a new type of Bchl-protein complex which showed a single absorption band in the near infrared region at 806 nm was obtained. The reaction center of strain OCh 114 was associated with a c-type cytochrome.

STUDIES ON THE INTERRELATIONSHIP AMONG THE INTENSITY OF A RAMAN MARKER BAND OF CAROTENOIDS, POLYENE CHAIN STRUCTURE, AND EFFICIENCY OF THE ENERGY TRANSFER FROM CAROTENOIDS TO BACTERIOCHLOROPHYLL IN PHOTOSYNTHETIC BACTERIA

Abstract Resonance Raman spectroscopy was used to study the polyene‐chain structure of carotenoids in light‐harvesting pigment‐protein complexes from purple photosynthetic bacteria. When major carotenoids of Rhodobacter sphaeroides were incorporated into the light‐harvesting complexes of Chromatium vinosum, they showed a relatively intense Raman band at 965 cm‐1 arising from the CH out‐of‐plane wagging modes of the polyene chain. This result was almost the same as that for the intrinsic carotenoids in Chromatium vinosum, but completely different from that for the intrinsic carotenoids in Rhodobacter sphaeroides. On the other hand, the intrinsic carotenoids of Chromatium vinosum lost the intensity of the 965 cm‐1 Raman band upon protein denaturation. These results support the view that the intensity of the 965 cm‐1 Raman band reflects distortion of the polyene chain, independent of its chemical structure. The polyene‐chain distortion is affected by the apoprotein to which carotenoids are bound. The distortion of the polyene chain is correlated with a decrease in the efficiency of the energy transfer from carotenoids to bacteriochlorophyll.

In vivo states and functions of carotenoids in an aerobic photosynthetic bacterium, Erythrobacter longus

In vivo states and functions of carotenoids in the membranes and the isolated RC-B865 pigment-protein complexes from an aerobic photosynthetic bacterium, Erythrobacter longus, are investigated by means of fluorescence excitation and resonance Raman (RR) spectra. Erythroxanthin sulfate, a dominant carotenoid species in the membranes (>70%), is found not to transfer the absorbed light energy to bacteriochlorophyll (Bchl), and its RR spectra are similar between the in vivo and in vitro states. These observations indicate that erythroxanthin sulfate does not interact with either Bchl or proteins in the membranes, and suggest that its function may be limited to photoprotection by quenching the harmful singlet oxygen. On the other hand, two other carotenoid species contained in the isolated RC-B865 complexes, zeaxanthin and bacteriorubixanthinal, have a high efficiency of energy transfer to Bchl (88±5%). The RR spectra of these two carotenoids, each of which can be selectively obtained by choosing the excitation wavelength, show some characteristics of interactions with proteins or Bchl.

Temperature dependence of the light-induced infrared difference spectra of chromatophores and reaction centers from photosynthetic bacteria

Abstract Temperature dependences of the light-induced infrared difference spectra have been observed between 300 and 80 K for chromatophores from several species of photosynthetic bacteria (Rhodobacter sphaeroides, Rhodobacter capsulatus, Chromatium vinosum, Rhodopseudomonas palustris and Rhodopseudomonas viridis) and for isolated reaction centers from Rhodobacter sphaeroides as well. Particular attention is paid to the light-induced (positive) bands in the C9 keto carbonyl stretching region, which are due to the radical cation of the bacteriochlorophyll special pair (P+). The observed bands are decomposed into two to four Gaussian curves, depending on the bacterial species. The positions of the resultant component bands are correlated with the degree of localization/delocalization of an unpaired electron over the two bacteriochlorophylls in the special pair on the time scale of infrared absorption (∼ 10−13 s). The intensities of most of the component bands show temperature dependences, which confirm the existence of multiple structures for the moiety involving P+ and its environment. The water contents in some samples affect the intensities of the light-induced bands. This effect depends on bacterial species as well as on the state of the sample (whether the sample is isolated RCs or chromatophores).

Femtosecond time-resolved coherent anti-Stokes Raman scattering from carotenoids in vivo and in vitro: comparison of vibrational relaxation times (T2) of the in-phase CC stretching bands

Abstract Femtosecond time-resolved coherent anti-Stokes Raman scattering has been observed from two carotenoids, rhodopin and spirilloxanthin, in vivo and in vitro. Intracytoplasmic membranes of a species of photosynthetic bacteria have been used as the in vivo sample where the carotenoids exist in the pigment—protein complexes. The vibrational phase relaxation rate in vitro is almost the same as that of β-carotene previously reported, but that in vivo is definitely faster.

31P-NMR studies of photophosphorylation in chromatophores from Chromatium vinosum

Abstract A light illumination system was designed for a 31P-NMR spectrometer and was applied for the analysis of time courses of photophosphorylation in chromatophores obtained from Chromatium vinosum by direct measurement of 31P-NMR. Internal and external pH values of chromatophores were estimated from chemical shifts of inorganic phosphate (Pi) resonances, and the rates of photophosphorylation were estimated from the relative intensities of α-phosphorus resonances of nucleotides. Light-induced NMR spectral changes during photophosphorylation reaction in chromatophores were analyzed on the basis of equilibrium described as ATP ⇄ ADP ⇄ AMP. The results suggest that the phosphorylation and dephosphorylation reactions were in equilibrium among all nucleotides in vivo. In particular, it was noted that ADP was produced from AMP in the photophosphorylation in chromatophores.

Structural Changes of the Bacteriochlorophyll Dimer in Reaction Centers of Photosynthetic Bacteria as Studied by Infrared Spectroscopy

Photosynthesis is the process by which light energy is utilized to synthesize chemical substances useful to almost all the living things on the earth. Charge separation, one of the most important processes in the light-energy conversion, takes place in the pigment-protein complex called “reaction center (RC)”, which consists of protein subunits, special pigments (generally chlorophylls), and several electron transport components. Recent X-ray crystallographic analyses have successfully visualized the organization of pigments (a special dimer of bacteriochlorophyll (BChl), two accessory BChl molecules, two bacteriopheophytin (BPhe) molecules, quinones and non-heme iron) as well as the structure of the protein subunits in the RCs.

Motions and structures of chromatophore of a photosynthetic bacterium (Chromatium vinosum) as revealed from carbon-13 and phosphorus-31 NMR

Carbon-13 enriched-chromatophore was prepared from a 13C-enriched culture of a photosynthetic bacterium (Chromatium vinosum) with a purpose to investigate the dynamic structures of photosynthetic membranes and proteins by 13C-NMR spectra which were observed in a relatively resolved state at 75.46 MHz (under a 7.05 T static magnetic field). This was in clear contrast with phosphorus-31 NMR spectra of chromatophore with broad band signals. The 13C-NMR was assigned to signals essentially from lipids (mostly phospholipids with a small amount of galactolipids). Linewidths of 13C-NMR signals of an intact chromatophore were narrowed on addition of detergents such as Triton X-100, sodium dodecyl sulfate (SDS), and lauryl-N,N-dimethylamineN-oxide (LDAO). Particularly the line-narrowing effect by Triton X-100 was remarkable among them. High resolution 31P-NMR spectra of phospholipid in a chromatophore were observed only in the presence of detergents. Spin-lattice relaxation times (T1s) of the lipid 13C-NMR signals in chromatophore indicate a low mobility of the polar head groups of the lipids, which was interpreted to indicate the presence of the interactions between the polar head groups of the lipids with proteins.