Electron Transport by Diffusible Molecules
In green plants, the slowest part of photosynthesis was detected by an experiment performed by Emerson and Arnold in 1932 in which leaves or cells were illuminated by a succession of very short flashes. It was found that the maximum rate of oxygen production or carbon dioxide uptake could be obtained with repetition rates of 100 per second, even though, with a flash duration of 10 µs, the plant was only receiving light for 1/1000 of the time. The slowest step was (much later) traced to the reduction of a C-type cytochrome, cytochrome f, by the plastoquinol formed by PSII. Cytochromes are relatively easy to observe since their sharp α-bands in the reduced state can be measured spectroscopically in the window between the blue- and red-absorbing peaks of the chlorophyll. Cytochrome f in the reduced state has its α-band at 554.5 nm.
KeywordsElectron Transport Photosynthetic Electron Transport Hydrogen Sulphide Purple Bacterium Green Sulphur Bacterium
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