PHOTOCHEMICAL REACTIONS OF PLASTOCYANIN 

 IN CHLOROPLASTS 



Sakae Katoh and Atusi Takamiya 



The idea that copper functions in photosynthesis in green plants was 

 proposed before it was shown to be present in the photosynthetic apparatus. In 

 1939, Neish first described the occurrence of copper in chloroplasts in a re- 

 markably high concentration when compared with the other metals present^ D. 

 In the same year, Green et al. showed that the photosynthetic carbon dioxide 

 uptake was markedly inhibit'ed by several reagents which were generally re- 

 garded as inhibitors of copper enzyme^^). The relatively high effectiveness 

 of these inhibitors, at concentrations which were completely without effect on 

 the dark respiration, led these authors to propose that copper is involved in 

 the photosynthetic reactions of chlorella. 



Since then, several reports appeared in confirmation of these earlier 

 results. Whatley et al. showed a high localization of copper in the chloroplast 

 fragments of sugar"beet(3). The sensitivity of photosynthesis and the Hill re- 

 action towards the copper-binding reagents has also been repeatedly confirmed 

 with chloroplasts(4, 5). Furthermore, Spencer and Possingham, working with 

 tomato plants, clearly demonstrated that copper is an essential micronutrient 

 for the development of chloroplast activity^^). 



Prior to the work reported here it was thought that the copper in the 

 chloroplasts was associated with those proteins which oxidize polyphenolsC^). 

 To date, however, there is no conclusive evidence for the participation of this 

 group of enzyme in the photochemical processes of chloroplasts. In addition 

 they are not ubiquitous in occurrence among photosynthetic plants and algae. 

 Moreover, when they are present, their concentration in the chloroplasts is 

 generally low and varies widely with different plants. 



Another type of copper complex, which we have recently discovered in 

 the chloroplasts, is a non-autooxidizable copper protein, plastocyanin^o). It 

 is proposed that this copper protein functions in the photochemical activity of 

 the chloroplasts. The aim of the present work is to summarize the general 

 properties of plastocyanin, as well as its distribution in photosynthetic organ- 

 isms. The results of our recent experiments on the effect of this copper 

 protein on several photochemical reactions of chloroplasts will be discussed. 



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