ROLE OF THE CARBON DIOXIDE ACCEPTOR IN INDUCTION 1415 



comes high enough for carboxylation to keep pace with the photochemical 

 utihzation of A -002. The resulting carbon dioxide induction loss will be 

 balanced by the "pick-up" (c/. ifig. 33.49a). 



As a second example, we can assume that the stead.y rate of photosyn- 

 thesis is dependent on [A -002], and that the rate of formation of A -002 is 

 determined entirely by the available quantity of the catalyst Ea. In this 

 case, oxygen liberation will show an "inverse induction" ; it will begin at a 

 higher rate and decline to a steady level. The carbon dioxide absorption, 

 on the other hand, may be practically constant, or show a slight increase to 

 a steady level. A pick-up will nevertheless occur, at the end of the light 

 period, to compensate for the excess oxygen liberated during the "inverse 

 induction" (cf. fig. 33.49b). A somewhat similar situation is postulated 

 in Shiau and Franck's interpretation of the second induction wave (sec- 

 tion 4). 



These are only two examples of induction effects that may arise if the 

 illumination causes a marked disturbance of the carboxylation equilibrium. 

 The shape of the pick-up curves should show whether, under the conditions 

 of the experiment, the carboxylation is of first order with respect to [A] (as 

 in fig. 33.49a), or of zero order (as in fig. 33.49b). The latter relation can be 

 expected, e. g., in cyanide-poisoned cells, where catalyst Ea is almost com- 

 pletely inactivated. (The extended duration of the pick-up in the pres- 

 ence of cyanide was noted by Auf demgarten ; cf. chapter 8, page 207.) 



Since the total quantity of the carbon dioxide acceptor appears to be of 

 the same order of magnitude as that of chlorophyll, a practically complete 

 decarboxylation of this acceptor should lead to the pick-up of about one 

 molecule of carbon dioxide per mole of chlorophyll (and to a corresponding 

 induction loss of carbon dioxide, or induction gain of oxygen). The dura- 

 tion of the pick-up should be, in the nonpoisoned state, of the order of 10 

 or 100 seconds. The frequency with which a chlorophyll molecule absorbs 

 quanta at the light intensity at which the pick-up becomes noticeable, 

 ~ 10,000 lux, is between 0.1 and 1 absorption per second; if 10 quanta are 

 needed to make an "occupied" molecule A available for a new carbon di- 

 oxide molecule, the mean life-time of the acceptor in the occupied state will 

 be between 10 and 100 seconds. In order that 50% of the complexes can 

 be dissociated in the steady state, the average time required for recarboxyla- 

 tion also must be between 10 and 100 seconds. 



In the EA-deficient (e. g., cyanide-poisoned) state, the pick-up can be 

 expected to last much longer; in this case, the depletion of A-C02(and 

 the corresponding increase of fluorescence, cf. chapter 28, page 1051) should 

 occur in light much weaker than 10,000 lux. 



Another reversible induction effect, which may or may not be associated 

 with the disturbance of the carboxylation equilibrium, is the liberation of 



