82 THE METABOLISM OF ALGAE 



in synthetic ability it is more appropriately considered here 

 rather than under the heading of heterotrophism. 



The first step in the assimilation of a-amino-acids, such 

 as glycine and alanine, is evidently deamination, so that 

 their nitrogen enters into metabolism as ammonia.^' ^ Thus 

 during the growth of Scenedesmus ohliquus in the light in a 

 medium containing glycine, which forms a good source of 

 nitrogen for this alga, considerable amounts of ammonia 

 are liberated.^ Since S. obliquus is able to grow slowly in 

 the dark with glycine as its sole source of carbon, it might 

 be that this excess ammonia is produced because the rate 

 of deamination of the glycine is high as a result of the 

 utilization of the carbon residue under conditions of carbon 

 deficiency. Evidently this cannot be so, since if glucose is 

 supplied together with glycine to illuminated cultures the 

 rate of deamination per cell remains the same, although less 

 ammonia appears in the medium because of the more rapid 

 growth of the alga. It appears, therefore, that deamination of 

 glycine by S. ohliquus is independent of carbon metabolism 

 and is in excess of requirements.^ In Chlorella vulgaris the 

 rate of deamination of this amino-acid is relatively slower 

 than in Scenedesmus and limits the rate of growth of the alga 

 with the result that no ammonia is liberated provided that 

 the medium is neutral.'* Similarly Chlorella, Haematococcus 

 and Zygnema spp. deaminate alanine relatively slowly so 

 that no ammonia is liberated from the cells, whereas 

 Ankistrodesmus, Stichococcus and Hormidium, are of the 

 same type as Scenedesmus and give off an excess of ammonia 

 to the medium when supplied with these amino-acids.^ 

 Bacterial deaminases have a maximum rate of reaction at 

 about pH 8-0 but the optimum for these algal deaminases 

 is on the acid side of neutrality, between pH 5 and 6.^- * 

 The algae in which deamination has been demonstrated 

 frequently occur in waters contaminated with organic 

 matter and must play a considerable part in the degradation 

 of nitrogenous substances in such situations. 



Aspartic acid, glutamic acid, asparagine, succinamide 

 and glutamine, have also been found to be suitable as sole 

 nitrogen sources for various green algae.®' ^' ^ Aspartic acid 



