1420 INDUCTION PHENOMENA CHAP. 33 



Eb, according to chapter 34) was found by Franck, Pringsheim and Lad to 

 be unaffected by inhibition. Inactivation of Eb should affect immediately 

 both carbon dioxide uptake and oxygen Hberation, but according to chapter 

 28 not the yield of fluorescence. 



The attribution of induction to the oxygen-liberating catalyst, the "de- 

 oxygenase" (catalyst C in Franck's terminology; Eq rather than Eq in 

 chapter 6 and chapter 9), is the remaining alternative; and it is sup- 

 ported by several pieces of evidence. In the first place, anaerobic incuba- 

 tion experiments with algae of the type of Scenedesmus have demonstrated 

 directly that, after a dark anaerobic period (and, a posteriori, probably 

 also after a dark period in air), the photochemical and catalytic mecha- 

 nisms of photosynthesis are still intact, with the exception of the oxygen- 

 liberating catalyst (since these algae are able to reduce carbon dioxide in 

 light if hydrogen is supplied as substitute reductant). 



Further arguments for the oxygen-liberating catalyst as the primary 

 cause of induction can be derived from experiments with hydroxylamine 

 (Vol. I, page 311). The latter appears to be a specific poison for the 

 oxygen-liberating enzyme system; its uniform effect on the rate in weak 

 and strong light leads to the surmise that this system is formed (or acti- 

 vated) by photosynthesis itself, and continuously deactivated by a dark reac- 

 tion, so that its stationary concentration adjusts itself to the prevailing 

 rate of photosynthesis. A catalyst of this kind obviously must be com- 

 pletely deactivated in the dark, and is thus likely to cause induction effects. 

 The "autocatalytic" formation of the "deoxygenase" explains the repeti- 

 tion of induction losses upon each successive increase of the steady rate of 

 photosynthesis (whether it is brought about by a change of light intensity, 

 temperature or carbon dioxide supply). 



Since we have assumed that the inhibition of catalyst Eb does not affect 

 fluorescence, one may ask why the same should not hold also for the inhibi- 

 tion of the oxygen-liberating catalyst, since the latter, after all, occupies a 

 similar "finishing" position in the scheme of photosynthesis. 



If we assume the validity of a scheme such as 7.IV, Eb and Eq assume 

 exactly symmetric positions, and inhibition of either of them should lead to 

 disappearance of the primary photochemical product (such as A -11002 or 

 HX and A' -OH or Z) by back reaction. Inhibition of the second catalyst 

 on the oxidation side, Eq, could, on the other hand, lead to the accumula- 

 tion of somewhat more stable intermediates (designated by { OH } 2 or { O2 } in 

 Vol. I). Franck suggested that these "photoperoxides," if not removed by 

 Eo (or by the hydrogenase in hydrogen-adapted algae), tend to react with 

 metabolic products (sugars?), converting the latter to substances capable 

 of "narcotizing" chlorophyll (as well as Eb). In this way, the "finishing" 

 catalyst, Eq, acquires the capacity of affecting indirectly the fluorescence of 



