1968 KINETICS OF PHOTOSYNTHESIS CHAP. 37D 



factory agreement with the data of Ehrmantraut and Rabinowitch (p. 

 1130) was obtained at pH 3 and 675 m/x; the yield was lower at other pH 

 values and declined at the shorter wave lengths, until a minimum was 

 reached at 575 m^t; it was higher again at 475 m^. 



Warburg (1952), using spinach chloroplasts and quinone as oxidant, 

 found quantum requirement as high as 70 at 400 mu, and 100 at 644 mM. 

 He considered this extremely low efficiency, as well as its dependence on 

 wave length, as striking demonstrations that the Hill reaction has nothing 

 in common with photosynthesis (the latter having, according to Warburg, 

 a quantum requirement of less than 3, independent of wave length). 

 Comparison with the results of Ehrmantraut and Rabinowitch (p. 1130) 

 and of Wayrynen shows that Warburg must have used a very poor, almost 

 inactive preparation — perhaps because the quinone concentration (0.05 M) 

 was far above the optimum (about 0.005 M, according to fig. 35.25). War- 

 burg also reported that his chloroplast preparation gave no reaction at all 

 with ferrocyanide. 



(/) Quantum Requirement of Bacteria 



Larsen, Yocum and van Niel (1952, cf. also Larsen 1953) measured the 

 quantum requirement of a species of green sulfur bacteria, Chlorobium 

 thiosulphatophilum, with thiosulfate, tetrathionate or molecular hydrogen 

 as reductant. With dense bacterial suspensions, the light curves of CO2- 

 consumption w^ere distinctly sigmoid; the same was true, albeit to a dis- 

 tinctly lesser degree, for light curves of the hydrogen consumption (com- 

 pare figs. 28.8 and 28.11; concerning the interpretation of sigmoid light 

 curves, see pp. 948 and 1126). Because of the inflection at the beginning 

 of the light curve, maximum quantum yield measurements on bacteria 

 were best carried out in dilute suspensions, and as high up the linear part 

 of the light curve as possible. 



Measurements were made in monochromatic light (interference filter, 

 ^max. = 732 mix), with absolute intensity measured by thermopile, and ab- 

 sorption by means of an integrating sphere. Yields were measured mano- 

 metrically, in 30-40 minute runs, eliminating from calculation the first 

 10 minutes of illumination, in oxygen-free nitrogen atmosphere containing 

 2-5% CO2. In ten experiments with H2 as reductant, quantum require- 

 ments of 7.8-11.8 were measured (average, 9.1); in eight experiments with 

 Na2S203, such of 8.9-11.4 (average, 9.3); and in five experiments with 

 Na2S406, such of 8.9-9.7 (average, 9.3). 



In this case, again, a quantum yield measurement on a new t3^pe of or- 

 ganism, having a different kind of photochemical metabolism, gave prac- 

 tically the same results as so many previous measurements on green plants, 

 chloroplasts and bacteria had given — between 8 and 10 quanta per four 



