THE CHEMISTRY OF PHOTOSYNTHESIS 



281 



e. Glycollic Aldehyde. 



The possibility that glycollic aldehyde may be an intermediate step in 

 the formation of sugar has been suggested by various workers ^^ and, as 

 has been stated, it has been regarded as a possil)le intermediate step in 

 the condensation of formaldehyde. Lob *^ observed that carbon monoxide 

 and w^ater under the influence of the silent electric discharge produce gly- 

 collic aldehyde and used this fact as the basis of a theory that the 

 latter substance may be an intermediate product in photosynthesis. 



Fincke ^" has developed a theory which is a departure from most others 

 in that he considers glycollic aldehyde one of the first reduction products 

 of carbonic acid. This viewpoint has certain distinct advantages over 

 the formaldehyde theory. Glycollic aldehyde is very easily condensed 

 to tetroses and hexoses in vitro and the condensation is known to take 

 place in the animal organism, while formaldehyde is notoriously poisonous 

 even in low concentrations and its condensation is not easily effected.®^ 

 Fincke also considers that glyoxylic acid, which has been found in plants, 

 may be related to photosynthesis. Of considerable interest in this theory 

 is the point that it takes into account the fact that oxygen is necessary 

 for photosynthesis. This is the action of a moloxide. Fincke calls it a 

 superoxide. He regards that some component of the chlorophyll reacts 

 with molecular oxygen : more properly this could be assumed to be a 

 component of the chloroplast or related to the enzyme for the existence 

 of which Willstatter and StoU have brought considerable evidence. At 

 any rate carbon dioxide is not reduced directly, but reacts first with another 

 substance : 



R+O2 



R. 



/ 



O 



\ 



o 



o 



R 



/ 



0=:C< 



\ 



+ 



o o = c< 



OH 

 OH 

 OH 

 OH 



OH 



R 



> 



C< 



o, 



OH 



OH 

 C< 

 I OH 



+ 



O, 



OH 



R 



/ 



C< 



\ 



OH 



R 



OH 



C< 





o — c< 



o 



H 

 OH 



H 



R 



/ 



o c< 



OH 



H 



C< 

 H OH 



\ 



+ 



O 



OH 



H 

 C< 

 HI OH 



Reinke, Bcr. chem. Gcs., 14, 2148 (1881). Lippmann, ibid., 24, 3306 (1891). 

 Lob, Landw. Jahrb., 35, 541 (1906) ; Biochem. Zeit., 63, 93 (1914). 

 Fincke, Biochem. Zeit., 61, 157 (1914). 

 Barrenscheen, Biochem. Zeit., 58, 300 (1914). 



