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Chloroplasts were isolated using aqueous and nonaqueous procedures.Aqueous chloroplasts lost approximately 50 per cent, of theirsoluble proteins during isolation. Nonaqueous chloroplasts retainedall their soluble enzymes, but lost their ability to performthe light reactions of photosynthesis. It was possible to reconstitutea chloroplast system of higher activity by adding soluble enzymesfrom nonaqueous chloroplasts to protein-deficient aqueous chloroplasts.The properties of the reconstituted chloroplast system wereas follows: 1. The CO2 fixation rate of the reconstituted chloroplast system( 4 µM./. chlorophyll/hr.) was 34 times that ofthe aqueous chloroplasts ( I µM./. chlorophyll/hr.). Thefixation of aqueous chloroplasts isapparently limited in partby lack of soluble enzymes. 2. During light-fixation, the reconstituted chloroplast systemaccumulated PGA. This indicates that the reduction of PGA totriosephosphate is a rate-limiting step in this system. 3. It was possible to increase the CO2 fixation to 12 µM.CO2/mg. chlorophyll/ hr. by addition of ATP and TPNH to thesystem, but the reduction of PGA was still rate-limiting. 4. Further increase in the fixation rate was obtained by concentratingthe reaction mixture. Part of the striking differences of theCO2-fixing capabilities of chloroplasts in vivo and in vitrois caused by dilution effects. Extrapolation of the dilutioneffect to the protein concentration which exists in chloroplastsyields a CO2 fixation rate of approximately 30 µM./mg.chlorophyll/hr. 5. Inhibitors which are located in vivo outside the chloroplastsaffect the CO2 fixation in vitro. 6. Under consideration of the examined factors which influencethe CO2 fixation of isolated chloroplasts, it is possible toraise the fixation from approximately 1 per cent, to at least15 per cent, of the fixation in vivo. 相似文献
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