INTRODUCTION II 



in which it has been sought, i.e. representatives of the 

 Chlorophyceae, Euglenineae, Phaeophyceae and Rhodo- 

 phyceae.^' ^^' ^*^' "^® Peroxidase and polyphenol oxidases 

 have been shown to be present in various algae ^^ but the 

 part which these enzymes play in respiration has not yet 

 been established. 



The transfer, storage and utilization of the free energy 

 released in respiration appears usually to be effected through 

 phosphorylated compounds. The best known example of 

 the formation of such compounds is one occurring in the 

 course of glycolysis in yeast, that in which the energy 

 released by the oxidation of the aldehyde group of 3-phos- 

 phoglyceraldehyde is used for the introduction of a new 

 phosphate group in the i- position with a relatively small 

 over-all change in free energy (see Fig. i). From the 

 I : 3-phosphoglyceric acid which is produced, the phos- 

 phate radical is transferred to adenosine diphosphate giving 

 adenosine triphosphate in which form it may be used for 

 the phosphorylation of other substances thus raising their 

 potential chemical energy content to the level necessary for 

 their participation in synthetic reactions.^^' *^ Certain of 

 the substances involved in the phosphorylation cycle of 

 yeast, e.g. hexose phosphates and phosphoglyceric acid, are 

 known to be present in Scenedesmus, Chlorella^^' ^^ and 

 Euglena.^ Adenosine triphosphate itself is perhaps absent 

 from Chlorella but phosphorylated compounds which may _^ 

 have a similar role are evidently present in this alga^^ 

 together with an enzyme capable of hydrolysing adenosine 

 triphosphate.^* Adenosine di- and triphosphates have been 

 identified in Eiiglena.^ The relative proportions of the 

 different phosphorus containing fractions in Chlorella alter 

 following illumination of the cells in a manner which sug- 

 gests that phosphorylated compounds are acting as energy 

 carriers. ^^* Evidence that the manner in which the energy 

 of phosphate bonds is utilized in synthesis is similar in 

 algae and in other organisms is available in the case of 

 starch or glycogen formation, in which the energy necessary 

 for the polymerization of glucose is provided from the phos- 

 phate bond of glucose- 1 -phosphate.^^' *^ Phosphorylases 



