Development of the Mode of Action 



of the Photocatalytic System 



in Organisms 



A. A. KRASNOVSKII 



A. N. Bakh Institute of Biochemistry , U.S.S.R. Academy of Sciences, Moscow 



FORMATION OF PHOTOCATALYSTS 



At present most plausible are those hypotheses which attribute the metabolism 

 of primary organisms to the assimilation of organic substances of abiogenic 

 origin [i]. Such organic compounds are sufficiently stable in usual conditions; 

 the activation of their transformation in living organisms could, in general, 

 have been achieved catalytically or photochemically. However, 'light' activation 

 is of advantage when there is need for energy 'storage', by conversion of the 

 energy of light quanta into the potential chemical energy of photoproducts. 



Processes thermodynamically spontaneous are efficiently activated cataly- 

 tically; present-day heterotrophic organisms extensively activate substrates by 

 catalysis. We may suppose that in utilizing energy-rich abiogenic organic com- 

 pounds, primary organisms employed a simple catalytic mode of activation, the 

 more so since they inevitably must have absorbed catalytically active substances 

 from the environment. Probably the primary biocatalysts were complexes of 

 amino acids, proteins, and porphyrins with metal ions or oxides, which are 

 readily absorbed and bound by these substances. Complexes of metals with 

 proteins, amino acids, and porphyrins could have ensured manifold 'dark' 

 catalytic transformations of organic substances, without the aid of 'light' acti- 

 vation. This type of biocatalyst is still predominant in organisms : iron, copper, 

 manganese, zinc, molybdenum, cobalt, and many other metals are essential 

 components of enzymic systems. 



Apart from the concentration of the elements and their compounds in the 

 Earth's crust, several other factors were probably important in the 'selection' 

 and absorption of inorganic compounds from the surrounding medium. Among 

 these factors were : the solubility of the compounds of an element in the bio- 

 sphere [2], its catalytic action in different complexes, the co-ordination number 

 of bound metal atoms, etc. 



It would be interesting to trace the possible stages in the formation of photo- 

 catalytically active pigments, and the changes in the mechanism of action of the 

 pigment system in the course of evolution from primary heterotrophs to the 

 autotrophic mode of life. But, unfortunately, in such an enquiry we cannot 

 draw upon reliable palacobotanic data; the most ancient known types of organ- 



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