• Journal of Microbiology and Biotechnology
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• v.8 no.6
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• pp.714-718
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• 1998

Various mutants either lacking or having decreased levels of light-harvesting complexes and reaction center complex were obtained with a high frequency by an increased formation of poly-3-hydroxybutyrate (PHB) in Rhodobacter sphaeroides. One of the photosynthesis-defective mutants, PY-17, which was devoid of any of the light-harvesting complexes (B800-850, B875) as well as the reaction center complex, was analyzed further. The mutant showed substantial transcription of the puhA, pufKBALMX, and pucBAC operons coding for the structural proteins of the photosynthetic complexes although each of the activities was lower than that of the wild type. Translation of the pufKBALMX and pucBAC operons were also active in the mutant although with activities different from the corresponding one of the wild type. From these results the mutation appears to exert its effect at the post-translational level of the photosynthetic complex assembly. Complementation of the photosynthesis-defective phenotype of the mutant was achieved with an about 12-kb DNA region containing the puhA gene. The relationship between the formation of PHB and photosynthetic complexes is discussed.

• Journal of Microbiology and Biotechnology
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• v.9 no.5
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• pp.604-612
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• 1999

A puc-deleted cell of Rhodobacter sphaeroides grows with a doubling time longer than 160 h under light-limiting photoheterotrophic (3 Watts [W]/㎡) conditions due to an absence of the peripheral light-harvesting B800-850 complex. A spontaneous fast-growing mutant, R. sphaeroides SK101, was isolated from the puc-deleted cells cultured photoheterotrophically at 3 W/㎡. This mutant grew with an approximately 40-h doubling time. The growth of the mutant, however, was indistinguishable from its parental strain during photoheterotrophic growth at 10 W/㎡ as well as during aerobic growth. The membrane of SK101 grown aerobically did not reveal the presence of any spectral complex, while the amounts of the B875 complex and photosynthetic pigments of SK101 grown anaerobiclly in the dark with dimethylsulfoxide (DMSO) were the same as those of the parental cell. These results indicate that the oxygen control of the photosynthetic complex formation remained unaltered in the mutant. The B875 complex of SK101 under light-limiting conditions was elevated by 20％ to 30％ compared with that of the parental cell, which reflected the parallel increase of the bacteriochlorophyll and carotenoid contents of the mutant. When the puc was restored in SK101, the B875 complex level remained unchanged, but that of the B800-850 complex increased. The mutated phenotype of SK101 was complemented with orfQ encoding a putative bacteriochlorophyll-mobilizing protein. Accordingly, it is proposed that the mutated OrfQ of SK101 should have an altered affinity towards the assembly factor specific to the most peripheral light-harvesting complex, which could be either the B875 or the B800-850 complex.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.858-864
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• 2014

Recently, many researches have shown that even photosynthetic light-harvesting pigment-protein complexes can have quantum coherence in their excitonic energy transfer at cryogenic and physiological temperatures. Because the protein supplies such noisy environment around pigments that conventional wisdom expects very short lived quantum coherence, elucidating the mechanism and searching for an applicability of the coherence have become an interesting topic in both experiment and theory. We have previously studied the quantum coherence of a phycocyanin 645 complex in a marine algae harvesting light system, using Poisson mapping bracket equation (PBME). PBME is one of the applicable methods for solving quantum-classical Liouville equation, for following the dynamics of such pigment-protein complexes. However, it may suffer from many defects mostly from mapping quantum degrees of freedom into classical ones. To make improvements against such defects, benchmarking targets with more accurately described dynamics is highly needed. Here, we fall back to reduced hierarchical equation of motion (HEOM), for such a purpose. Even though HEOM is known to applicable only to simplified system that is coupled to a set of harmonic oscillators, it can provide ultimate accuracy within the regime of quantum-classical description, thus providing perfect benchmark targets for certain systems. We compare the evolution of the density matrix of pigment excited states by HEOM against the PBME results at physiological temperature, and observe more sophisticated changes of density matrix elements from HEOM. In PBME, the population of states with intermediate energies display only monotonically increasing behaviors. Most importantly, PBME suffers a serious issue of wrong population in the long time limit, likely generated by the zero-point energy leaking problem. Future prospects for developments are briefly discussed as a concluding remark.