1582 



PHOTOCHEMISTRY OF CHLOROPHYLL 



CHAP. 35 



supported by Tolmach's observation of a rapid (nonphotochemical) oxida- 

 tion of added TPNH2 by spinach juice. 



At this point (following a suggestion by Vennesland and Conn), Tol- 

 mach added to the chloroplast suspension the complete malic enzyme sys- 

 tem (instead of TPN alone), to provide a "trap" for TPNH2. In unsep- 

 arated, chloroplast-bearing cell juice, the addition of TPN, pyruvate, car- 

 bonate, Mn + + salt and "malic enzyme" did not enhance the oxygen yield 

 more than did TPN alone; but in precipitated, washed and resuspended 

 chloroplast material, a small, but marked, stimulation was observed (figure 

 35.19D). If PGA was added together with the malic enzyme system, the 

 extra oxygen burst was about double that with pyruvate alone. 



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TIME (MINUTES) 



Fig. 35.19D. Stimulation of photochemical O2 evolution from 3 mm.^ chloro- 

 plast suspension (1.8 ^g Chi) containing 0.04 ^mole MnCl., 0.17 Mmole pyruvate, 

 0.4 Mg- TPN, 0.08 fimole glycylglycine buffer (pH 7.0), by addition (at 21 min.) 

 of 2 mm.3 malic enzyme, and switching on the light (at upward arrow) (Tolmach 

 1951). Gas: 4.2% CO2 in N2; flow 8.8 cm.Vmin., 25° C. 



To complement the demonstration of oxygen evolution from the malic 

 enzyme system by a demonstration of concurrent CO2 fixation, tracer 

 C*02 was used. Some C*02 fixation could be observed in light even in the 

 absence of malic enzyme; it was tentatively attributed to exchange reac- 

 tions. Addition of malic enzyme increased the fixation by a factor of five, 

 making it about equivalent to the extra oxygen production observed phos- 

 phorometrically under the same conditions. 



The Chicago investigators did not attach to the pyruvate reduction, 

 mediated by TPN in illuminated chloroplast suspensions, the same impor- 

 tance as did Ochoa and Vishniac, who saw in it evidence of the actual mech- 



