THE TEMPERATUEE INSENSITIVE OXIDATION OF CYTOCHROME F IN GREEN 

 LEAVES - A PRIMARY BIOCHMICAL EVENT OF PHOTOSYNTHESIS 



Britton Chance and Walter D. Bonner, Jr. 



The temperature insensitive oxidation of a cytochrome compon- 

 ent adjacent to chlorophyll has proved to be an incisive tool in 

 the study of the basic mechanisms of primary photo-reactions at 

 the biochemical level. In the context of this paper the "primary" 

 light-induced reaction is that which involves a chemical step, 

 and therefore we exclude the physical processes by which chloro- 

 phyll may become activated. 



A number of aspects of the temperatiire insensitive oxidation 

 of cytochrome c in the purple sulfur bacteria Chromatium have 

 been siommarized elsewhere (l), and special attention has recent- 

 ly been paid to the fact that the reaction is not only temp- 

 erature insensitive but is also viscosity insensitive (2). The 

 application of this method to green plants has not previously 

 been very fruitful. While H. T. Witt has recorded the low temp- 

 erature oxidation of cytochrome f, the observation has been re- 

 stricted to chloroplast suspensions and, in fact, to chloroplast 

 suspensions which are specifically treated with sucrose in order 

 that the effects be observed (3). As yet no observations have 

 been made of the low temperature response of cytochrome f in the 

 intact leaves of green plants, although numerous observations 

 have been made at room temperature in leaves and in suspensions 

 of algae; for example, Chlorella {k) , Anacystis (5) and Porphy- 

 ridiiom (6)and in chloroplast s (T). 



This paper describes the application of the double-beam spec- 

 trophotometer to the detailed quantitative study of cytochrome f 

 oxidation at 77 K in a variety of leaves. The experimental 

 res\alt allows an evaluation of the role of cytochrome f oxidation 

 in relation to the"PYoo" absorption band. In addition, we pro- 

 vide an accvirate representation of the relationship between light 

 absorption in chlorophyll a and the rate of cytochrome f oxida- 

 tion in leaves. 



Materials . 



The materials used were market spinach leaves, leaves plucked 



66 



