242 



REDUCTION OF CARBON DIOXIDE 



CHAP. 9 



with Smith's results (1943) described in chapter 3, page 37), and a httle 

 (about 0.06%) went into chlorophyll {cf. page 557). The fate of the 

 large residue remained obscure. 



More extensive experiments were carried out with Chlorella suspen- 

 sions by Ruben, Kamen, Hassid, and Devault (1939), Ruben, Kamen, 

 and Hassid (1940), and Ruben, Kamen, and Perry (1940). Figure 24 

 shows that the uptake of radioactive carbon in light proceeds for over 



an hour at a constant rate of about 

 0.22 ml, C*02 per min. per milliliter 

 of cells (in the dark, saturation was 

 reached after 0.2 ml. was taken up in 

 a single exposure to C*02 or 0.8 ml. in 

 repeated exposures and evacuations; 

 cf. Fig. 27). Manometric measure- 

 ments proved that all radioactivity 

 acquired in light was caused by as- 

 similation of carbon dioxide (and not 

 by an exchange of radioactive carbon 

 for ordinary carbon). This was con- 

 firmed by experiments with cyanide 

 and urethane, which showed identical 

 effects on carbon dioxide absorption 

 and on the increase of radioactivity. 

 In attempts to identify the fate of the 

 absorbed radioactive carbon, Ruben 

 and coworkers made numerous "co- 



50 

 Time, minutes 



Fig. 24. — Uptake of radioactive 

 carbon in light. The radioactive-car- 

 bon content of the algae is expressed 

 in arbitrary units, one unit correspond- 

 ing to the uptake of 6.3 mm.^ carbon 

 dioxide per mm.^ of algae (after Ruben, 

 Kamen, and Hassid 1940). 



precipitation" and " coextraction " 

 tests, which are customary in the work 

 with small quantities of matter. After 

 illumination periods of 1-5 min., they 

 rapidly killed the cells, extracted them 

 with water, and added different "car- 

 rier substances." They found, in this 

 way, that the active intermediate product formed in such short exposures 

 is not identical with formaldehyde, acetaldehyde, propionaldehyde, gly- 

 colaldehyde, glyceraldehyde, methanol, ethanol, glycol, glycerol, erythrol, 

 glucose, sucrose, starch, hexose monophosphate, glycine, alanine, arginine, 

 histidine, albumin, acetone, or with any of the following acids : formic, acetic, 

 propionic, butyric, oxalic, succinic, malic, citric, maleic, fumaric, glycolic, 

 pyruvic, glyceric, tartaric, lactic, ascorbic, glucuronic, glutamic, aspartic, 

 and glutaric. Fractionation experiments showed that the active inter- 

 mediate is not volatile at 120° C. It is soluble in water (at least to the 

 small extent required to account for results obtained with very dilute 



