SOME GENERAL KINETIC CONSIDERATIONS 871 



(26.1) CO: + A . ' ^ ACO2 — > A + {HCO2} 



(i. e., a reversible binding of carbon dioxide by an acceptor A followed by 

 reduction of the complex ACO2 by a photochemically produced reductant 

 {H}) leads to a "Bose type" system of curves P = /[CO2] (where Pis the 

 rate of the over-all reaction). If carboxylation is so rapid (compared with 

 photosjTithesis) that its equilibrium is not disturbed even in strong light, 

 these "carbon dioxide curves" will be hyperbolae, which diverge from the 

 origin, and remain in a constant ratio up to saturation. Saturation corre- 

 sponds, in this case, to complete carboxylation of all the available acceptor, 

 and is therefore reached at the same value of the variable [CO2] in all 

 curves. The saturation rate rises with increasing concentration of the 

 reductant {H} (and therefore also with light intensity, since w^e assume 

 that { H } is produced by light) . 



We will further see that, if carboxylation is a slow process the rate of 

 which is proportional to [CO2], a [C02]-proportional "roof" is imposed on 

 the rate of the over-all reaction, namely : 



(26.2) Pmax. = A-„Ao [CO2] 



where Ao is the total concentration of the acceptor*, and ka the rate 

 constant of carboxylation {cf. equation 26.1). We will show that, because 

 of this "roof," the curves P = f [CO2], which would otherwise begin with 

 the slope k^Ao {i. e., which would stay just inside the "permitted area") 

 will be reduced to an initial slope half as large, i. e., kaAo/2. More gener- 

 ally, curves that, without limitation, would have begim with a slope ak^Ao 

 will be reduced to an initial slope k^Aoa/(a + 1). Thus cui-ves that in 

 the case of rapid carboxylation would begin with slopes between 10 k^Ao 

 and 100 kaAo, would all be confined, in consequence of slow carboxylation, 

 to slopes between 10/11 fc^Ao and 100/101 fc„Ao, and would thus present a 

 "Blackman picture." If the carboxylation product, ACO2, in equation 

 (26.1) has to undergo a monomolecular transformation before it can react 

 with {H}, this would impose a [C02]-independent ceiling on the rate of the 

 overall reaction, namely : 



(26.3) Pmax. = kiAo 



where ki is the rate constant of the postulated monomolecular transforma- 

 tion, and Ao the total available quantity of A. As a result of this "ceiling," 

 the curves P = f [CO2], which would otherwise reach a saturation value of 

 P = kiAo, will be reduced to a saturation level half as high, P = A;iAo/2. 



* We omit square brackets in the designation of constant concentration, i. e., we 

 write Ao, Chlo, etc., instead of [A]o, [Chl]o, etc. 



