593 



Lester Packer 



tides. Parallel studies on the viscosity of the protein extract 

 made in the presence and ahsence of the nucleotides did not show 

 a decrease in viscosity with added nucleotides, which would te 

 expected if this preparation behaved like the contractile proteins 

 of manms.lian muscle and mitochondria. Also the substrate specifi- 

 city of the chloroplast protein extract \ms examined; hydrolysis 

 of ATP,ITP, ADP, pp. and p-nitrophenyl phosphate occurred indica- 

 ting a rather non-specific phosphatase activity. These results 

 differ from those for light activated ATPase in whole chloroplasts 

 (18), which are unable to hydrolyze phosphate compounds other than 

 nucleoside triphosphates. Either the exti-acted protein fraction 

 represents a different nucleoside triphosphatase or non-specific 

 phosphatase, or alternatively extraction of this material from the 

 chloroplasts leads to a change in its properties. In view of 

 these differences, it is difficult to decide on the precise rela- 

 tionship of this extracted material to the action of ATP and ITP 

 in chloroplasts without further study. 



DISCUSSION AND CONCLUSIONS 

 The findings presented here demonstrate that ATP exert a defi- 

 nite effect on the scattering responses of chloroplasts which is 

 related to its light activated hydrolysis. It is also demonstra- 

 ted that the conditions required for photophosphorylation are 

 capable of promoting scattering changes in chloroplasts in res- 

 ponse to actinic light. Thus two possible routes may exist for 

 these effects in chloroplasts. Referring to the diagram illus- 

 trated in figure 6, the present results may be explained by 

 analogy with the energy transfer pathway by mitochondria in the 

 folloid.ng fashion. The photosynthetic electron transfer pathvray 

 would lead to the production of a series of intermediates, the 

 earlier non-phosphorylated intermediates eventually becoming 

 phosphorylated, and by interaction with ADP leading to the synthe- 

 sis of ATP. In view of the results with light activated ATP 

 hydrolysis, including the action of reactants such as ADP and 

 ammonia, the site in the dark energy transfer pathway most closely 

 associated with scattering changes may well be located in the 

 region of the non-phosphorylated intermediates, before the termi- 

 nal stages where ATP synthesis and hydrolysis would take place. 

 The marked inhibitory effect of ammonia on scattering responses 

 but not on ATP hydrolysis after it has been light-activated 

 supports the notion that this region of the energy transfer path- 

 way, close to the electron transport system, is involved with the 

 scattering changes and that this is the region which is affected 

 by ammonium ions. 



Should this analogy between similarity in the dark energy 

 transfer reactions in mitochondria and chloroplasts be further 



