SELF-NARCOTIZATION 1041 



Another consequence of the assumption of an eight times repeated action of the 

 catalyst Eb is that the estimate of the ratio E°/Chlo, must be reduced from 1 : 2000 to 

 1:250 (cf. chapter 34). 



(/) Analytical Formulation: Narcotization 



Franck has evolved the concept — repeatedly referred to above — of in- 

 ternal regulation of photosynthesis by "self-narcotization." This self- 

 narcotization occurs, according to Franck, whenever excess light, or lack of 

 reactants, or presence of poisons, make the photochemical apparatus de- 

 ficient in normal substrate, and creates the danger of this apparatus "run- 

 ning amok" and destroying valuable cell components (including itself). 

 The specific form of this protective mechanism, envisaged by Franck, 

 consists in the formation of a "half-oxidized" metabolite (a plant acid?), 

 which is adsorbed on chlorophyll, blanketing all or part of it, preventing its 

 photosensitizing activity and incidentally enhancing itS fluorescence. We 

 will derive kinetic equations for a simple "servomechanism" of this type, 

 to see whether it can introduce fundamental changes in the shape of the 

 light curves of photosjmthesis (and fluorescence). 



We consider the following mechanism: 



X-Chl-HZ _±^ XH-ChlZ 



XH-Chl-Z(+{C02l) J^Z^ [HCOo} + X-Chl-Z 



X-Chl-Z (+{H201) J^IZ:^ X-Chl-HZ + {OH} 



(28-47Fa) X-Chl-HZ (+ ICO2! + {H2O!) > JHCO2! + tOH} + 



X-Chl-HZ 



K 

 (28-47Fb) {OHl + E > EOH 



A-e' 



(28.47Fc) EOH > E(+ O2) 



K 

 (28-47Fd) I OH} + X-Chl-HZ (+ H,M) > X-Chl-HZ-HM -|- H2O 



(= {Chi} + H2O) 



K 

 (28.47Fe) X-Chl-HZ-HM (+ 10.) > X-Chl-HZ (+ M + IHaO) 



where {Chi} is an abbreviated expression for the "narcotized chlorophyll," 

 XChl-HZ-HM. 



The components in parentheses are supposed, for the sake of simplifica- 

 tion, to be present in excess and to react practically instantaneously, so 

 that their concentrations do not appear in kinetic equations. The summa- 

 tion of the first three equations gives equation (28.47Fa) for the primary 

 photochemical process. It is further assumed that the reduction product. 



