82 



H. T. WITT 



ferricyanide) going on or not (Fig. 8a and h). But using phenol- 

 indophenol and other dye« as a Hill oxidant the decline is strongly 

 dependent on the concentration of this substance. At concentrations 

 of '~10~'* mole per liter it is possible to shorten the lifetime of the 

 change of absorption (at constant temperature) by a factor of about 

 ten. The effect is reversible. One explanation for this effect may be the 

 following: the unknown substance Z is replaced by phenol-indophenol, 

 which reacts directly with Y. Because phenol-indophenol is reduced, 



c: 

 .o 



I- 

 o 

 <o 



OJ 



c: 

 o 



01 



chloroplasts 



without 



Oxidants 



chloroplasts 

 with ~ IQ-'-M/ltr 

 Chinon 



chloroplasts 

 with~!0'^M/ltr 

 2,6- Dichlor phenol- 

 indophenol 



50 W'^sec 



time 



Fig. 8. Change of absorption of chloroplasts (spinach, pH = 6.5) as function of 

 time under different conditions. U = 10 ~^ second, t,i = 1.0 second. Temperature 

 13.5°C. 



Y can be a reduced substance and X the oxidized form. We hope to 

 learn more about the primary process l)y exploring this possibility of 

 interfering with the reaction system in chloroplasts. 



The results of these experiments are of a preliminary character 

 After further experiments we shall make a detailed comparison of 

 these effects with the results of other authors. I hope to have demon- 

 strated that, by means of the method which was used in all these ex- 

 periments, it is possible to measiu'e reaction patterns of the primary 

 process from '^10 ~* second up to the time required for the reduction 

 phase of the Hill reaction. 



