PHOTOCHEMISTRY OF LIVE CELLS 



1625 



500 



450 



400 



350 



- 300 



- 250 



200 



150 



60 

 MINUTES 



Fig. 35.29. Isotopic tracer evidence of closed-circle Hill reaction in live 

 Anahaena cells in carbonate buffer No. 11. Respiration (1.73 mm.'/miu.) and 

 CO2 reduction poisoned by cyanide (0.01 mole/1.). The only effect of light (6.5, 

 1.5, 26 klux) is 1:1 isotopic exchange of O between O2 and H2O (after Brown 1953). 



light (whose rate remains considerably higher than that of unpoisoned dark 

 respiration, cf. figure 35.29). It seems most likely that the photochemical 

 exchange mechanism is in these cells — and by inference, in other species 

 as well — the one suggested by Mehler for chloroplasts: a Hill reaction 

 leading to hydrogen transfer from H2O to O2, converting the latter to H2O2, 

 followed by the catalatic decomposition of the peroxide. 



Horwitz (1954^) found that substitution of deuterium oxide for ordinary 

 water reduces the rate of quinone reduction by Chlorella at all hght intensi- 

 ties, and not only in the light-saturated state, as is the case with photosyn- 

 thesis {c,J. p. 296). 



Bibliography to Chapter 35 



A. Photochemistry of Chlorophyll Solutions 



1943 Pepkowitz, L. P., J. Biol Chem., 149, 465. 



Baur, E., and Niggli, F., Heh. Chim. Acta, 26, 251, 994. 



