19 



B. Rumberg, P. Schmidt-Mende, J. Weikard aud H.T. Witt 



top of fig. 2. It shows changes around 7o$ mu (dotted line) and 

 in addition oxidized cytochrome (solid line). The cytochrome is 

 masking changes around 45o mu which may be caused by other sub- 

 stances. Addition of reduced PMS (phenazine methosulf ate) (as- 

 corbic acid in excess), prevents the trapping of oxidized cyto- 

 chrome (bottom in fig. 2). Under these conditions a difference 

 spectrum can be seen at -15o which is similar to that of a), 

 b ) , and c ) . 



e) A fifth method is described in 7,b). 



2. Kinetics 



During the flash the absorption decreases very fast (-i. 1o sec 

 in chlorella). In the dark a backreaction takes place in~1o~ 

 sec at 2o^C (fig. 5a, 6a) (4)(5). 



5. Identification of Ghl-a j 



The upper results (5 equal spectra under different conditions) 

 suggest that the changes at ^5o mu and 7o3 mu are caused by one 

 substance. This was additionally proved by comparing the kinetik 

 behaviour of both changes in reactivated aged chloroplasts under 

 different conditions. The lifetime and the magnitude are identi- 

 cal at both wave-lengths at different values of pH (4) (fig. 5) 

 and also at different concentrations of added reduced PMS_(^). 

 Decreases of absorption changes just with the two absorption 

 bands of chlorophyll-a indicate that very probably a chlorophyll 

 -a (Chl-aj) is in action (-4-). 



4. Oxidation of Chl-a j 



That the decreases of absorption indicate an oxidation of Chl-a^ 

 in the light, was provided in our experiments by the fact that 

 in aged chloroplasts reduced PMS or reduced DPIP (2,6-Dichlor- 

 phenol-indophenol) can be directly coupled to the light product 

 (4)(1). This is demonstrated by the strong acceleration of the 

 decay time with increasing concentrations of red PMS or red 

 DPIP (fig.-M-) and by the demonstration of a first order reaction 

 (fig. 4). The electron-acceptor of Ghl-aj is called Z. Obviously 

 in aged chloroplasts photooxidized Chl-a-j- is directly reduced by 

 electrons provided from red PMS: 



Z ^r^ Ghla-j- < red PMS 



(The arrows indicate the flow of electrons). 



5. Ohl-a-r - oxidation as a primary act 



The production of Ghl-a-. within -i 1o~5 sec and the trapping at 

 -15o G give evidence th4t this oxidation is a primary act (4). 



5. The effect of far red background light 



Far red actinic light between 7oo and 72o mu can only oxidize 

 Ghl-a-,- (2) (in chlorella and fresh chloroplasts with Kill-oxi- 

 dantsj. Actinic light with wave-length -c 7oo mu results in an 

 oxidation of Chl-a-p followed by a reduction of Ghl-at • There- 

 fore light of <. 7oo mu is obviously channeled into two reaction 



