CARBON DIOXIDE FIXATION 289 



that a large proportion of the protein of the ehloropiast was extracted 

 by the water treatment. The ability of the broken chloroplasts to fix 

 CO2 was partially restored when the water extract of chloroplasts was 

 added back to the residual particles, as shown in Table I. As with 

 whole chloroplasts, CO2 fixation by the broken ehloropiast system was 

 strictly dependent on illumination. 



TABLE I. Effect of Chloroplast Extract (CE) on Photosynthetic Carbon Dioxide 

 Fixation by Broken Chloroplasts (Piw) (4) 



C'^Oj fixed (c.p.m.) 



The water extract of chloroplasts was found to contain a number of 

 enzymes. Those so far identified are : 



phosphorylase menadione reductase 



amj'lase pentose phosphate isomerase 



phosphoglucomutase phosphoribulokinase 



hexose phosphate isomerase carbox\'Iatmg enzyme (5) 



aldolase transketolase 



TPN- and DPN-dependent triosephosphate dehydrogenases (6). 



The addition to the broken chloroplasts of DPN, TPN, and ATP, 

 singly or in combination, failed to restore their capacity for CO2 



TABLE II. Effect of Adenosine Triphosphate (ATP) and Di- and Triphospho- 



pyridine Nucleotides (DPN and TPN) on the Fixation of C^Oa by Broken 



Chloroplasts Supplemented with a Water Extract of Chloroplasts (CE) (4) 



