already suggested under "Carboxylic Acids" four ways in 

 which acetate, or acetyl CoA, could be made. These were: (1) 

 splitting of malic acid to glyoxylate and acetate, (2) reduction 

 of glycolic acid to acetate, (3) oxidation of pyruvic acid to 

 acetyl CoA, and (4) dehydration and phosphoroclastic split- 

 ting the postulated glycolyl-enzyme complex from transketo- 

 lase reaction of the carbon reduction cycle to give acetyl phos- 

 phate. We favor the last way as being the most likely. How- 

 ever, if only the first three of these pathways are available, 

 the third is probably the most important. 



However the acetate is formed, it is rapidly converted 

 to fats in the light in algae. Experiments with Scenedesmus 

 photosynthesizing in the presence of acetate- 1-C^^ and C^^02 

 (14) demonstrated a light-accelerated incorporation of ace- 

 tate into fats. A similar light-enhanced incorporation of ace- 

 tate-2-C^* into lipids by Euglena was found by Lynch and 

 Calvin (95). Sissakian (96) demonstrated the synthesis of 

 higher fatty acids from labeled acetate in chloroplasts from 

 sunflower plants. The utilization of free acetate in the light 

 by chloroplasts is to be expected, since there is an abundance 

 of ATP in the photosynthesizing chloroplasts for the conver- 

 sion of acetate to acetyl phosphate and thence to acetyl CoA. 



The scheme of fatty acid synthesis proposed by Wakil 

 and Ganguly (97) for the formation of fatty acids from 

 acetyl CoA in animal tissues has been widely accepted. A 

 similar pathway may exist in photosynthetic tissues. This 

 pathway is incorporated in the hypothetical scheme of fat 

 photosynthesis shown in Figure 9. Wakil (98) and Wakil and 

 Ganguly (99) report that the first step in the synthesis from 

 acetyl CoA is a carboxylation to give malonyl CoA. This step 

 requires biotin and ATP, as well as Mn+ + . Malonyl CoA and 

 acetyl CoA then condense to give acetoacetyl CoA, which 

 then undergoes a series of reductive steps to give eventually 

 butyryl CoA and carbon dioxide (97). 



Although the work of Ganguly and Wakil has been with 

 animal tissues, it appears from the studies of Stumpf and 

 co-workers (100-103) that similar systems of fatty acid syn- 



57 



