64 THE METABOLISM OF ALGAE j 



in the case of acetic acid.^^ Similarly, results have been 

 obtained in experiments on the oxidative assimilation of 

 glucose by Chlorella pyrenoidosa in accord with the follow- 

 ing equation:^^^ 



C6Hio06+02->5(CHoO)+C02+H20 . . (14) 



These equations, implying a definite relationship between 

 oxidation and assimilation, suggest that the nature of the 

 intermediate products of the decomposition of the substrate 

 may be more important in determining the proportion 

 which is oxidized than the energy relationships involved.^* 



However, the proportion of substrate which is oxidized 

 is not as fixed as these results suggest. Not only does the 

 proportion vary from species to species but it may alter in 

 the same organism according to its physiological condition^* 

 or the reaction of the medium.^^i If it is supposed that a 

 substrate for oxidative assimilation is first converted into 

 fragments which can enter the metabolic pool then in most 

 cases these fragments will be of one sort and the propor- 

 tions oxidized and used for synthesis will depend on energy 

 requirements and the conditions to which the organism is 

 exposed. For example, it is to be expected that in the oxida- 

 tive assimilation of glucose the normal glycolytic pathway 

 wall be followed and that this substance after phosphoryla- 

 tion to yield hexose phosphates may then be used in poly- 

 saccharide synthesis or be further degraded and enter the 

 metabolic pool as phosphoglycerate. The various pathways 

 by which phosphoglycerate may be metabolized are indi- 

 cated in Fig. 10. There is no evidence that glucose is 

 assimilated by algae in any other way; the possibility sug- 

 gested by equation 14, for example, that in oxidative 

 assimilation it is converted to pentose by oxidation and 

 decarboxylation receives no support from analytical data.^^i 



A further example that may usefully be discussed is that 

 of acetate, a substrate which, as we have already seen, is 

 the most generally utilized by algae. There are several pos- 

 sible ways in which this substance might enter into meta- 

 bolism. Acetate, by reductive carboxylation, might yield 

 pyruvic acid. However, the oxidative decarboxylation of 



