Studies of pigment compositions in photosynthetic bacteria, and, The in vitro reconstitution of Lhca4 apo-protein with chlorophyll d.

摘要

Chlorophylls (Chl) and bacteriochlorophylls (Bchl) play important roles in photosynthesis. They are responsible for light harvesting, energy transfer and electron transfer in prokaryote and eukaryote photosynthetic machineries. Identification of photosynthetic pigments will aid to understand the structure of these machineries and the intrinsic properties of these pigments. For this purposes, pigment compositions of two marine photosynthetic prokaryotes, the Salton Sea isolate of a chlorophyll-d containing cyanobacterium and the green filamentous anoxygenic phototroph Chlorothrix halophila were analyzed. The Salton Sea isolate is a marine cyanobacterium whose cell extract shows a maximum absorption at 697 nm similarly to Acaryochloris marina, a Chl d-producing organism that was discovered previously. This pigment has had significance in studies of evolutionary origins of oxygenic photosynthesis because of its unique spectral characteristic that it absorbs the far-red light relative to the light absorbing of Chl a which has a very similar chemical structure to Chl d.;On the other hand, C. halophila found in Baja California Sur, Mexico absorbs solar light energy even further red. C. halophila is a green filamentous phototrophic bacterium that grows anaerobically. This organism has a unique light harvesting apparatus called chlorosomes that contains up to hundreds of thousand of aggregated and protein-less Bchl c. Nonetheless, Bchl a, a photosynthetic pigment carried out the charge separation and electron transfer in the reaction center, has not been identified in Chlorothrix halophila. The pigment composition analysis of these organisms will provide a closer look at the major pigments that constitute the photosynthetic apparatus of this organism.;Since cyanobacteria have similar photosynthetic machineries to plants, we investigated the intrinsic properties of the light harvesting pigment in plant photosystem I antenna complexes by substituting Chl a and Chl b with Chl d. The outcome of this investigation will contribute to a new area of photosynthesis studies in which engineering of new crops permits them to absorb light at lower energy by incorporating Chl d. This will allow plants to take advantage of regions of the electromagnetic spectrum that are now not utilized.