1. Fixation of Carbon Dioxide 



The ** Background" CO2 Fixation Occurring in Green 

 Cells and Its Possible Relation to the Mechanism 



of Photosynthesis 



SHIGETOH MIYACHI, TOYOYASU HIROIvAWA, and HIROSHI 



TAMIYA, The Tokugawa Institute for Biological Research, and Department 



of Botany, Faculty of Science, University of Tokyo 



When preilluminated algal cells are brought into contact with 

 Ci^02 in the dark, C^^ is fixed in two different ways (1,2). One is a 

 fixation caused by some photogenetic agent (s), and the other is a 

 background fixation which occurs also in nonpreilluminated cells. 

 It may be reasonable to assume that different agents (or systems of 

 agents) are acting in these two kinds of CO2 fixation. Let us denote 

 the photogenetic agent (s) by R and the agent (s) acting in the back- 

 ground fixation by D. It has been shown (3,4) that, whereas the re- 

 action between R and C^^02 proceeds very fast and is completed 

 within about 30 seconds at 25 °C., the reaction between D and €^"02 

 is considerably slower. If the radioactivity fixed by D is denoted by 

 r, it is almost a linear function of the time of contact of cells with 

 C^*02 in the dark; namely, dr/dt = k[D], or r = kt[D]. The relative 

 concentration of D in nonpreilluminated cells can be gauged by 

 measuring the radioactivity (r) fixed within a definite time of con- 

 tact of cells with 0^*02 in the dark. The level of R in preilluminated 

 cells can be determined by measuring the C^* fixation in 30 seconds 

 since, within such a short period, the C^* fixed by the background 

 capacity is negligible. If the exposure to C'^02 is longer, say 5 minutes, 

 background fixation becomes significant and the C^* fixed will be the 

 sum of a rapid light-induced action of R and a slower almost linear 

 background fixation attributable to D. By subtracting the radio- 

 activity fixed in 30 seconds from that fixed in 5 minutes, we can de- 

 termine the background C^^Oa-fixing capacity (on 5 minutes basis) 

 existing in preilluminated cells. Using these methods, we investi- 



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