616 A. A. KRASNOVSKli 



reasonable to assume that the development of the abihty to produce oxygen 

 from water required the utilization of two quanta of light for the transfer of a 

 single electron, i.e., the conjugation of two elementary photoprocesses to over- 

 come the high energy barrier in the path of the transfer of a single elearon 

 (hydrogen) from water to carbon dioxide, whereas in bacterial photosynthesis 

 one elementary photoprocess (using a single quantum of hght) is sufficient for 

 the transfer of a hydrogen atom from the hydrogen donor AH» to CO2. 



The two-stage electron transfer necessitated a more elaborate coupling with 

 enzymic systems and the formation of a 'stock' of intermediate hydrogen 

 donors. 



One can envisage the development of the following stages: (i) transfer of an 

 electron from water to an intermediate electron acceptor (e.g., cytochrome; 

 polyphenols, dehydroascorbic acid, or disulphides), that is, the Hill reaction, 

 (2) transfer of the electron from the reduced forms of these compounds to pyri- 

 dine-nucleotides taking part in the reactions of carbon dioxide reduction (e.g., 

 in the step phosphoglyceric acid - triosephosphate, according to the Calvin 

 scheme). Above we have considered the 'short circuiting' of the second stage of 

 hydrogen transfer by coupling with oxidative phosphorylation. The tentative 

 nature of these suggestions is due to the fact that there is as yet no definite 

 answer to the question as to whether the transfer of a single electron (hydrogen) 

 in photosynthesis requires one or two quanta [19]. 



THE STATE OF PHOTOCATALYTIC PIGMENTS 



As stated above, the utilization of solar energy by organisms necessitated the 

 large-scale synthesis of pigments so as to absorb a considerable portion of the 

 photochemically active part of the solar spectrum. Present-day organisms as a 

 rule contain substantial amounts of pigments. Chlorella, for example, contains 

 up to 5% of chlorophyll. 



In a study of the process of accumulation of chlorophyll when aetiolated 

 seedUngs become green we observed in collaboration with L. M. Kosobutskaya 

 the following picture of changes in the state of the chlorophyll [37]. Under the 

 action of light, protochlorophyll is converted to the primary 'monomeric' form 

 of chlorophyll, combined with proteins and lipids, which exhibits an absorption 

 maximum at 670 m/t and has a low fight stabifity. In the process of further 

 formation and accumulation of chlorophyll in the granules, the absorption 

 maximum gradually shifts to 678 m/i, which is characteristic of highly concen- 

 trated, oriented and light-stable forms of chlorophyll. These observations are in 

 keeping with the data obtained by T. N, Godnev and J. H. C. Smith [38]. 



By means of spectral methods we have studied the state of chlorophyll and 

 bacteriochlorophyll in various organisms from the phylogcnetic viewpoint, and 

 arrived at the following conclusions. The peculiar absorption spectrum of 

 bacteriochlorophyll in the cells of photosynthetic bacteria is due to aggregation, 

 to the orderly packing of bacteriochlorophyU in the granules; the absorption 

 spectrum of this pigment in sofid films and colloid solutions corresponds to the 

 spectra of living bacteria [39]. 



The chlorophyll in red and blue-green algae, and in green plants, is mainly 



