286 w. visiiNiAo 



cates that a major portion of the activity resided in a fraction pre- 

 cipitable at 0.2 to 0.5 saturation of ammonium sulfate. In a similar 

 series of experiments with dandelion lea\'es most of the activity could 

 be precipitated at 0.1 to 0.3 saturation of ammonium sulfate. The 

 oxidized product formed in this reaction is unknown. 



150-- 



100 - = 



-- 



H \ 1 1- 



10 



20 30 UO 50 lanutes 



Fig. 1. Potential changes in the hght. Reaction mixture: 1.0 ml. extract of 

 chloroplast acetone powder in 0.05 M K-PO4, pH 7.0, containing 1.0 mg. protein; 

 p-quinone, 1 mg.; to which was added later ethanohc extract, 0.05 mg. chloro- 

 phyll. Temperature, 15°; illumination, incandescent spotlight; time in minutes 

 0, dark, flushed with No; 5, hght turned on; 10, chlorophyll added; 18, light off; 

 23, N2 replaced with O2; 31, Oo replaced with N2 and light turned on. 



The activity determined by the enzymatic assay appears to paral- 

 lel reducing activity which can be determined potentiometrically (1). 

 A reaction vessel containing a platinum-calomel electrode pair was 

 used, in which 2 to 3 ml. of a reaction mixture could be stirred by a 

 continuous stream of gas. With quinone the results shown in Fig. 1 

 were obtained before the platinum electrode was ruined. Since the 



