238 



CONTROL MECHANISMS IN CELLULAR PROCESSES 



interpretations that follow concerning these effects are certainly very 

 tentative. 



2, 4 Dinitrophenol (DNP), an uncoupler of oxidative phosphory- 

 lation, had a marked effect in the case shown here. A repeat of this 

 experiment (not illustrated) gave no effect. This kind of result was 

 encountered many times and requires explanation. Note that the 

 phase shift which occurs, whatever it may be, is stable from one day 

 to the next. 



1^ 



J^: 



J^ 



i; 



J^i 



D|'8 L 06dim-»|'8 



- )-chloramph 



-\dnp sho-^m 



:} 

 :} 

 :] 

 3 



enicol 10" M 



PCMB 2 -10 M 



arsenite 9 ■< 10 M 



cyanide gxlO"" M 



_:» light 

 --►control 



06 



18 06 



18 06 If 



06 



Fig. 9-6. Several of the compounds shown here have pronounced and ap- 

 parently specific phase-shifting effects. Note in particular the marked effect of 

 arsenite in this regard. (See text and legend to Fig. 9-5 for details.) DNP = 

 2,4 dinitrophenol; PCMB — p-chloromercuribenzoate. 



With p-chloromercuribenzoate (PCMB), an inhibitor of sulf- 

 hydryl groups, there was a marked phase shift. In this case, how- 

 ever, the pattern was somewliat similar— but not exactly the same— in 

 the second run, as illustrated. Photosynthesis was strongly inhibited 

 by PCMB at these concentrations. 



Arsenite, an inhibitor of dithiol compounds, gave similar results 

 in four separate experiments, two of which are shown. Arsenite is 

 by far the most effective of the compounds tried by us, and a more 

 detailed study of this may lead to significant findings. 



Cyanide has a marked effect upon the cells and upon the phase, 

 but, as in the case of DNP, this phase-shifting effect is quite variable. 



The marked variability such as we note here with DNP and cya- 

 nide was also observed in the presence of compounds such as KCl 

 and AgNO.3. It seemed necessary to run a large number of controls 



