Energy Conversion in Photosynthetic Processes Page: 4 of 21
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Gordon Tollin, po-wer B, sgo, and Mel-In 'CatVin
Radiation Labo atory and Department of 2he i try
U university of California, Berkel :y, CaUfornia
March 10, 1958
The chemical pathway by which carbon is transformed from its ow-nrg7
form, carbon dioxide, into its high -energy form, principaly carbohydrao, Iles
been fairly completely mapped by use of tracer carbon, and our parent kn i.-8
of it is exhibited in Fig. 1. The photochemical apparatus that p-o-ides thi e-9
force for running the carbon cycle from Co toward polysaccharide, deslgnz a:
[E; in Fig. 1, is contained in the chloroplaits of green plants and in the
chromatophores of the simpler organiams auch as photosynthetic bacteria and
blue-green algae. The microstructure of this apparatus has been investigated
down to the level that may be reached with an electron microscope, and such an
electron micrograph is shown in Fig. 2. The universal appearance of these
ordered structures in all photosynthetic equipment suggests that the primary
quantum conversion occurs in a quasi-crystalline phase. One might be justifi d
therefore, in speaking of the primary quantur conversion in photosynthesis as
photophysical operation rather than a photochemical one.
KatzI in 1949, and, independently, Brad"_ey and Cal.vin2 in 1955, suggested
that aggregates of chlorophyll molecules is the chioroplasts might give rise to
conduction bands in which photoproduced electrons and holes could migrate. Such
a system would have the advantage of providing for a separation of the oxidizing
and reducing entities known to be necessary for photosynthesis.
This concept has remained purely speculative until, quite recently, a
number of researches have been ?ubl:shed which suggest that something of this
nature may indeed take place within chloroplasts. In 1956, Commoner and co-
workers published evidence for the presence of a light-induced electron-spin
resonance ESR) in spinach chloroplasts due to the photoproduction of unpaired
electrons. Again, in 1957, these workers have shown the presence of two kinds
of unpaired spins, one of which is transformed into the other. 4 In 1957, Arnold
and Sherwood studied dried chloroptast films and found them to exhibit semi-.
conductivity and thermnoluminescence, 5 In addition, some studies by Strehler
and co-workers have demonstrated the existence Qf temperature-dependent, long-
lived luminescences in algae and in chloroplasts. -9 Finally, the photo-
conductivity of chiorophyll films has been observed. 10
Our own experiments in this area began in 1956 with the demonstration by
Sogo of a light-induced ESR signal in dried eucalyptus leaves. Inasmuch as
these results iere rather poorly reproducibl.e it was decided to study isolated
chloroplasts , 1 Furthermore, when it became apparent that the spin-resonanco
signas decayed fairly rapidly when the light was turned off, the possibility that
at least part of the energy associated with these unpaired spins might appear as
luminescence '.d us to a study of the light-emission properties of the chloroplaet:
The rk cr be in hs paer iwas spn ored by the U. S. Atomic Energ y
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Tollin, Gordon; Sogo, Power B. & Calvin, Melvin. Energy Conversion in Photosynthetic Processes, report, March 10, 1958; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc878144/m1/4/: accessed January 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.