HILL REACTION IN FLASHING LIGHT 



1479 



molecules chlorophyll) per flash. In these experiments, the energy of the 

 flashes was increased by raising the discharge voltage to 5.8 kvolt; in the 

 higher range of energies the flash yield of photosynthesis appeared quite 

 constant between 30 and 80 (rel. units), indicating true saturation (c/. 

 above, section B2) ; no equally convincing proof of complete flash saturation 

 of the Hill reaction was possible in the accessible energy range. 



In contrast to photosjoithesis the Hill reaction in Chlorella showed no 

 induction loss in flashing Hght. 



Fig. 34.27. Flash saturation of photosynthesis and quinone reduction 

 by Chlorella (Ehrmantraut and Rabinowitch 1952). 



Gilmour, Lumry and Spikes (1953, 1954) made flashing hght experi- 

 ments with chloroplast preparations from Beta vulgaris, using ferricyanide 

 as oxidant, and an oxidation-reduction electrode as measuring device. 

 The chloroplast suspension was stirred during the measurement. Flash 

 illumination was provided by a 1000 watt incandescent lamp, and chopped 

 by rotating sectors. The brightness at the vessel was up to 250 klux; with 

 flashes lasting usually 2.8 msec, and in some experiments up to 16 msec, 

 the flash energy was as high as 700, and sometimes even 4000 lux sec. 



The largest flash yields observed were of the order of four Fe(III) atoms 

 reduced (corresponding to one O2 produced) per 3000 chlorophyll mole- 

 cules — a yield considerably below the Emerson-Arnold maximum. How- 

 ever, the maximum rate of Hill reaction in steady hght was, in Gilmour's 



