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ENERGY CONVERSION BY PHOTOSYNTHETIC REACTION CENTERS

Objective

PHOTOSYNTHETIC LIVING ORGANISMS ARE HIGHLY EFFICIENT IN CONVERTING SOLAR ENERGY INTO CHEMICAL POTENTIAL. THE UNDERSTANDING OF THEIR STRUCTURE AND ENERGY INTO CHEMICAL POTENTIAL. THE UNDERSTANDING OF THEIR STRUCTURE AND MODE OF FUNCTIONING SHOULD GIVE US USEFUL GUIDES TO DESIGNING SOLAR ENERGY CONVERTERS. WE PROPOSE TO BRING A SIGNIFICANT CONTRIBUTION TO THE ANALYSIS OF GREEN PLANT REACTION CENTERS, WHICH ARE THE MICROSCOPIC CONVERTERS OF ENERGY CONVERSION FROM PHOTONS TO CHEMICAL ENERGY. THE RECENT CRYSTALLIZATION OF BACTERIAL REACTION CENTRES HAS PERMITTED AN ENORMOUS ADVANCE IN THE KNOWLEDGE OF THEIR STRUCTURE. PLANT REACTION CENTRES ARE MORE COMPLEX, BUT THEY OFFER MAJOR ADVANTAGES IN RELATION WITH OUR OBJECTIVES, SINCE THE PHOTOSYSTEM-I CENTRE REDUCES LOW-POTENTIAL CARRIERS CAPABLE OF REDUCING H+ INTO MOLECULAR HYDROGEN, AND THE PHOTOSYSTEM-II CENTRE OXIDIZES A COMPLEX CAPABLE OF OXIDIZING WATER INTO GASEOUS DIOXYGEN.

THE FIRST PERIOD OF THIS RESEARCH PROGRAMME HAS BEEN DEVOTED ESSENTIALLY TO EXPERIMENTAL WORK ON THE REACTION CENTERS OF PHOTOSYSTEM-I AND II AND OF PHOTOSYNTHETIC BACTERIA. MOST OF THE PROJECTS HAVE ONLY BEEN STARTED. SOME EFFORT HAS AIMED AT PREPARING THE FUTURE STEPS OF THIS PROJECT BY BUILDING A FLASH ABSORPTION SPECTROPHOTOMETER WITH NANOSECOND TIME RESOLUTION AND LEARNING METHODS OF MOLECULAR BIOLOGY, THROUGH A STAY OF TWO SCIENTISTS IN LABORATORIES WHICH ARE WELL KNOWLEDGEABLE IN THESE METHODS.

THE RESEARCH ON PHOTOSYSTEM-II HAS BEEN CONDUCTED ESSENTIALLY ALONG TWO LINES. THE COMPARISON BETWEEN THE QUINONIC ELECTRON ACCEPTORS OF PS-II AND OF PURPLE BACTERIA HAS BEEN DETAILED BY EPR STUDIES. THE SHAPES OF EPR LINES OF QA- AND QB- HAVE BEEN COMPARED IN PS-II, IN RHODOSPIRILLUM RUBRUM AND IN RHODOPSEUDOMONAS VIRIDIS. THE DATA ARE STILL BEING ANALYZED, BUT THEY SHOW THAT THE COMPARISON EXTENDS INTO THE DETAILS OF THE SPECTRA, INDICATING VERY CLOSE STRUCTURAL RELATIONSHIP. THE SECOND APPROACH, WHICH IS ONLY AT ITS BEGINNING, IS A FLASH SPECTROSCOPIC STUDY OF THE REACTION CENTER OF PS-II, WHICH HAS BEEN ISOLATED RECENTLY BY A JAPANESE GROUP AND KINDLY MADE AVAILABLE TO US. THE PRIMARY BIRADICAL P+I- HAS BEEN OBSERVED AND SEVERAL PROPERTIES STUDIED: ABSORPTION SPECTRUM, LIFETIME, EFFECT OF MAGNETIC FIELDS AND OF TEMPERATURE, DECAY INTO A TRIPLET STATE. THIS WORK TENDS TO INDICATE THAT THE PAIR OF POLYPEPTIDES D1 AND D2 EFFECTIVELY CARRIES THE REDOX CENTERS INVOLVED IN PRIMARY PHOTOCHEMISTRY.

PHOTOCONVERSION BY THE PS-1 REACTION CENTER HAS BEEN STUDIED MAINLY THROUGH A STUDY OF THE PRIMARY BIRADICAL (P-700+, A0-) AND OF THE SECONDARY ONE (P-700+, A1-). BOTH STATES HAVE BEEN OBSERVED AT LOW TEMPERATURE AND THE INTERACTIONS BETWEEN RADICAL SPECIES HAVE BEEN STUDIED IN DETAIL. A NEW BIOLOGICAL MATERIAL HAS BEEN INTRODUCED IN THE LABORATORY, THE CYANOBACTERIUM SYNECHOCYSTIS, FROM WHICH PS-I PARTICLES HAVE BEEN PREPARED. THIS MATERIAL IS NOW UTILIZED TO DETERMINE THE ROLE OF VITAMIN K1 AS ELECTRON ACCEPTOR, BY EXTRACTION-RECONSTITUTION EXPERIMENTS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Commissariat à l'Energie Atomique (CEA)
Address
Centre D'études De Saclay
91191 Gif-sur-yvette
France

Participants (1)

INSTITUT DE CHIMIE
France
Address

Strasbourg