A key event was the elucidation
of the mechanism of chlorophyll participation in that process. In 1956 two important papers were published on this subject. Kok (1956), in the Netherlands, discovered that a small number of chlorophyll molecules (less than 1 %), characterized by light-induced absorbance changes at 700 nm, are involved in redox transitions, representing the energy trap (the reaction center). The other paper was from the Evofosfamide chemical structure research group of Eugene Rabinowitch in USA (Coleman et al. 1956). Here, ‘light-minus-dark’ difference spectrum reflecting changes in spectral region of chlorophyll absorption with a maximum at 680 nm was observed. In 1963, Krasnovsky and coworkers (Karapetyan et al. 1963) and Rubinstein and Rabinowitch (1963) showed that light-induced changes, observed in Coleman et al. (1956), were OSI-906 cost due to changes in fluorescence
excited by the measuring beam. The idea about redox transitions of small amount of chlorophyll (called later as a primary electron donor in reaction center) in oxygenic photosynthesis was soon established, an idea that we owe to Duysens (1952) for the reaction center in bacterial photosynthesis. Later the mechanism of the primary charge separation in the photosynthetic reaction centers was established in the studies of Krasnovsky and his colleagues. It was shown that bacteriopheophytin is the primary electron acceptor in photo-induced charge separation www.selleckchem.com/products/pexidartinib-plx3397.html in the reaction centers of purple bacteria (Shuvalov et al. 1976; Klimov
et al. 1976), pheophytin in the reaction centers of PSII (Klimov et al. GNE-0877 1977), and chlorophyll a in the reaction centers of PSI (Fenton et al. 1979; Nuijs et al. 1986; Shuvalov et al. 1986; also see Wasielewski et al. 1987). Krasnovsky suggested that chlorophyll aggregation may be one of the important factors controlling the formation of different chlorophyll forms in chloroplasts. Low temperature long-wavelength fluorescence found for concentrated solution of chlorophyll a was taken to indicate that a chlorophyll aggregate may be responsible for long-wave emission (see a review by Krasnovsky 1992). Long-wavelength chlorophylls were observed in vivo for the first time in green bean leaves as an emission band at 730 nm in the 77 K fluorescence spectra that was related to the aggregated chlorophyll (Litvin and Krasnovsky 1957). The long-wavelength emission, discovered by Brody (1958) in the green alga Chlorella, was ascribed by him to be from a ‘chlorophyll dimer’. Infra-red spectroscopic investigations of chlorophyll films provided evidence that aggregation indeed can occur in solid pigment films (Krasnovsky and Bystrova 1986). The idea was developed that an aggregation of pigments is involved in both the red shift and the fluorescence quenching of chlorophylls in vivo. Similar ideas were developed in Joseph Katz’s laboratory (Katz 1990).