INA.CTIVATION OF CATALYTIC SYSTEM AS CAUSE OF INDUCTION 1421 



chlorophyll — a change that can be caused directly only by preparatory cata- 

 lyst. (This hypothesis already was used in chapter 24.) 



The totality of the events in the "first wave" of induction is attributed 

 by Franck and co-workers (1941, 1945, 1947) to the photochemical produc- 

 tion of an "internal narcotic." One may ask: Why introduce an un- 

 known metabolite as an intermediate, and not assume direct action of the 

 "photo-peroxides" on chlorophyll? The answer is: first, that a "block- 

 ade" of chlorophyll by oxygen-precursors would be unlikely to lead to a 

 reduction in the rate of oxygen liberation (although it may produce a delay 

 in carbon dioxide uptake, and an upsurge of fluorescence) ; second, the 

 strong dependence of the first wave on species, age, culturing and conditions 

 that prevailed during the dark period points to the intervention of meta- 

 bolic products. 



One puzzling question in connection with the "first wave" of induction 

 is: How can a photochemical reaction lasting only 0.5 to 1 second, and 

 thus permitting, at best, only one chlorophyll molecule in ten or fifty to 

 absorb a quantum, bring about complete cessation of gas exchange, and 

 an increase in fluorescence yield by as much as a factor of three? 



As far as the chemical inhibition is concerned, a plausible answer can 

 be provided by reference to a catalyst the concentration of which is much 

 lower than that of chlorophyll. Flashing light experiments led to the 

 conclusion (c/. chapters 32 and 34) that this is true of the finishing catalyst, 

 Eb- This catalyst appears to be present normally to the extent of about 

 one molecule per 400-2500 molecules of chlorophyll. Franck and co- 

 workers pointed out that the amount of the internal narcotic produced 

 within a half second of moderate illumination is likely to be sufficient to 

 inhibit all of catalyst Eb, and thus to cause practical cessation of photo- 

 synthesis. 



If this picture is correct, then, in the first moment of illumination, car- 

 bon dioxide consumption should begin at a comparatively high level, cor- 

 responding to the full rate of the primary photochemical process, while the 

 liberation of oxygen should begin at a rate determined by the amount of the 

 active deoxygenase. Unless illumination is very weak (in which case the 

 residual amount of the oxygenase suffices to maintain the initial rate, and 

 no induction wave occurs), the initial rate of oxygen liberation is much 

 lower than that of the primary photochemical process. As a result, inter- 

 mediate oxidants accumulate, and within a second inhibit practically all 

 Eb (through the intermediary of the oxidizable metabolite), and thus stop 

 more or less completely both the formation of oxygen and the consumption 

 of carbon dioxide. According to the hypothesis used before, respira- 

 tion removes the "narcotic" poison — into which the metabolite produced in 

 the dark is converted in light — and thus causes the inhibition wave to sub- 



