REACTION OF CHLOROPHYLL WITH CO 2 47 



This change to a formaldehyde peroxide compound (III.) may 

 be illustrated as follows : 



It is true that experiments in vitro have entirely failed to 

 demonstrate the formation of a peroxide compound by means 

 of horseradish peroxidase, but this is considered to demonstrate 

 the essential difference between test tube experiments and the 

 activity of the living cell. There is no doubt that chlorophyll 

 in the chloroplast is protected from photo-oxidation or 

 decomposition by carbon dioxide in a way that chlorophyll in 

 colloidal solution in vitro is not, since the chloroplast will 

 tolerate concentrations of carbon dioxide which decompose 

 chlorophyll in colloidal solution to the magnesium free com- 

 pound phaeophytin (V.) with precipitation of magnesium 

 carbonate as illustrated by the equation 



C M H n O B N 4 Mg + H,0 + C0 2 = C 55 H 74 5 N 4 + MgCO 3 



V. 



Such a peroxidic compound (I II.) as is postulated above should 

 be fairly easily capable of losing oxygen either in one or in 

 two stages with regeneration of unaltered chlorophyll and 

 formation of formaldehyde (IV.) 



f>N 



R ;:v-Mg.O.C^ - R Mg+0+HCHO 

 1>NH 



Within the living cell the decomposition of the peroxide 

 formaldehyde compound (III.) is assumed to be brought about 

 by an enzyme, the existence of which enzyme is supported by 

 the following experimental evidence. 



