1584 



PHOTOCHEMISTRY OF CHLOROPHYLL 



CHAP. 35 



tailed composition is given in the caption. The reaction rate in this figure 

 corresponds to about 8 molecules oxygen evolved per molecule chlorophyll 

 per hour in light of about 28 klux — about 5% of the saturation rate of 

 photosynthesis. This yield, although considerably larger than that ob- 

 served by Vishniac and Ochoa, is still quite small. Furthermore, accord- 

 ing to curve I, the oxygen formation stops alter the evolution of only about 

 10~® mole oxygen from 10""^ mole pyruvate. 



20r 



a 



3 



•a 

 o 



fee 

 O 



t6 IQ 



Fig. 35.19E. Curve/: O2 evolution from chloroplast fragments (0.5 mg. Chi) 

 in light in the presence of 2 X 10 -« mole KCI, 2 X 10-« mole NaHCOj, 2 X 10-« 

 mole MnClo, 1 X 10"^ mole li pyruvate, 6.5 X 10"^ mole TPN, and 0.2 ml. "malic 

 enzyme" preparation from the same leaves. Total volume 3 ml.; 15.1° C, 28 

 klux. Curve II: same without malic enzyme. Curve III: same without TPN. 

 (Arnon 1951.) 



Arnon and Heimburger (1952) added to the above-described study a chromato- 

 graphic proof of the formation of tagged i-malate in the chloroplast-pyruvate-radiocar- 

 bonate-malic enzyme system. The estimate of C *02 fixed in malate indicated a stoichio- 

 metric equivalent of 4.5 mm.' oxygen; manometric measurement showed, in this par- 

 ticular case, an evolution of 18 mm.^ O2 in the complete system and of 15 mm.' O2 in an 

 aliquot from which malic enzyme was omitted, and in which practically no C" was fixed. 

 The difference (3 mm.' O2) is in satisfactory agreement with the value calculated from 

 C'^ fixation; but the very large O2 evolution in the blank (not shown by curve II in 

 figure 35.19E) makes the experiment somewhat unsatisfactory. 



