215 



Brian Colman and Wolf Vishnlac 



the hydroxyl tritium to the side chain. Upon reoxidation the label 

 would therefore be located on the phytol side chain. In a model 

 experiment, purified Co Q from Chromatiiom was reduced with NaBHj^ 

 in the presence of TOH, reoxidised with silver oxide, and reiso- 

 lated. The retention of tritium by the Co Q to the extent of half 

 the specific activity of the TOH, confirmed the possibility of 

 labeling the q.uinone by the mechanism which Dr. Calvin had 

 proposed. 



The methanol fraction contains six, and the water fraction 

 two chromatographically separable, but unidentified compounds, all 

 of which incorporate more tritium in the light than in the dark. 



Although we cannot explain the accumulation of tritium in the 

 isooctane fraction, the inhibition by CMU of tritium incorporation 

 into photo synthetic pigments is a further indication that tritium 

 can serve as a useful tracer in the investigation of photo synthetic 

 events. 



Table 1. Incorporation of tritium by chloroplasts 

 in the presence of CMU. 



Figures in c.p.m. The reaction mixture contained chloroplasts 

 (5 mg chlorophyll) in sucrose-potassivma phosphate, pH 7, 100 mC 

 H^OH, and CMU (lO"%) where indicated. Total volume 1.0 ml. 

 Temperature 10°C. 



