1026 



THE LIGHT FACTOR. I. INTENSITY 



CHAP. 28 



ko 



-^ HX-ChlHZ + A'R 



-> X-Chl-HZ + AHCO2 



(28.21b) HX-Chl-Z + A'HR 



(28.21c) HX-Chl-HZ + AGO. 



(28.21d) AHCO2 + A'R 



In this case, the main form in which the chlorophyll complex accumu- 

 lates during intense photosynthesis is the reduced form, HX-Chl-HZ. 



k' 



-> ACO2 + A'HR 



CO, 



X-CHIHZ 



+ A 



(^a) 



(28.21a) 



k' 

 (28.21a') 



AGO, 



HXChIZ 



HgO (or HR) 

 + A' 



A'H20(orA'HR) 



L 



J 



r 



HXChlHZ 



r) ((28.2lb) 



A'HO(or A'R) 



r 



AHCO2 



fr/)((28.2lc) 



1 



X- Chi- HZ 



(£-9) 



r 



)Q 



(28.2ld) 



(Ec) 



A -I- COa 



+ HzO 



(£■0) 



A ■^ (CHgO}^ A'H-Og (orA'-hR) 



Scheme 28.IB. Photosynthesis according to equations (28.21a-d). 



We chose above equation (27.6) as starting point of our considerations 

 (and not a similar equation for the reaction of the light-activated complex 

 with the oxidant A'H20), and are now interested, first of all, in the possible 

 interdependence of A* and [ACO2], caused by the primary back reaction. 

 Therefore, mechanism (28.20) is more convenient for our purpose than 

 mechanism (28.21), (because in 28.20 the primary back reaction, 28.20a', 

 competes directly with the reduction of [ACO2]). 



