INACTIVATION OF CATALYTIC SYSTEM AS CAUSE OF INDUCTION 1419 



light period, and of an autocatalytic adjustment of its concentration in 

 light to the level needed to maintain photosynthesis at the rate corre- 

 sponding to the prevailing light intensity. The role of the carbon dioxide 

 acceptor in the induction phenomena thus appears in a new hght, in par- 

 ticular in the interpretation of those features of induction (such as the ap- 

 proximate independence of its duration of light intensity) that point to a 

 factor activated in light only to the level sufficient to maintain the rate of 

 the over-all reaction sequence at the level permitted by other limiting reac- 

 tions. 



4. Inactivation of the Catalytic System as the Primary Cause of Induction. 

 Gaffron-Franck Theory of Induction 



The assumption that the inactivation of one definite catalytic agent in 

 the dark is the prime cause of the short induction period of photosynthesis 

 was first made by Gaffron (1937, 1939, 1940), and later developed into a 

 detailed theory by Franck and co-workers (1941, 1945, 1947, 1949). This 

 theory represents the most comprehensive attempt to date to explain the 

 induction phenomena, and we will give an account of it here, although in 

 many details it is speculative, and new observations — particularly that 

 of the autocatalytic formation of the carbon dioxide acceptor, and the 

 consequences this may have for induction — may call for its re-examination. 

 It must be kept in mind that the theory attempts to explain only the two 

 waves of inhibition which characterize the short induction period and not 

 the "bursts" and "gulps" of oxygen and carbon dioxide. (Franck has 

 endeavored to interpret the latter in terms of invasion of the photosynthetic 

 mechanism by respiration intermediates, as described in section 5 below.) 



Gaffron suggested that the cause of irreversible induction losses is the 

 inactivation of the oxygen-liberating catalyst (or catalysts). We recall 

 that kinetic researches, beginning with those of Blackman, Warburg, and 

 Willstatter and Stoll, led Franck and Herzfeld to contemplate three major 

 catalytic factors in photosynthesis — a carboxylating catalyst (Ea), a "fin- 

 ishing" (or "stabilizing") catalyst (Eb) and one (or more likely, two; c/. 

 chapter 6, page 133) oxygen liberating catalyst (Eq, and Eq in schemes 

 9.III, etc. 



That the carboxylase, Ea, is not rate-limiting during the initial period 

 of induction is shown, for example, by the insensitivity of the gas exchange 

 and fluorescence during this period to cyanide (cyanide is a specific inhibi- 

 tor for Ea). 



Catalyst Eb, too, is not limiting at the beginning of induction. This 

 has been demonstrated particularly clearly in anaerobic incubation experi- 

 ments, where the yield per flash (determined by the available amount of 



