CHLOROPHYLL AND ENERGY 185 



The change from mahc acid to pyruvic acid, because it 

 oxidizes carbon of one valency, produces energy and is accom- 

 plished theoretically without difficulty; the opposite process 

 needs energy. The presence of an appropriate diastase enables 

 the reaction to take place; it can be effected in one direction 

 or the other according to the conditions of the environment. 



Evans discovered in pigeon liver this diastase, the malic 

 diastase, which, through its apodiastase, is specially adapted 

 to mahc acid. Its active part, its codiastase, is triphospho- 

 pyridine nucleotide, sometimes oxidized (TPN) and sometimes 

 reduced (TPNH2). 



This malic diastase is added to a medium composed of 

 pyruvate, carbon dioxide, salts of manganese and TPN. 

 Hydrogen is provided by the addition of glucose-6-phosphate 

 and a special diastase, dehydrogenase, which will decompose it, 

 liberating hydrogen at the same time as the energy necessary 

 for the reaction. By means of the malic diastase, this liberated 

 hydrogen wiU be fixed with the carbon dioxide on the pyruvate 

 to give rise to malate. 



Such a reaction can be accomplished in the animal organism 

 but it can also be accompUshed, as we have seen, through 

 chlorophyll, which will provide the necessary energy, not only 

 for the fixation of carbon dioxide, but also for the liberation of 

 hydrogen from water. In the presence of carbon dioxide, 

 TPN, salts of manganese and mahc diastase, pyruvate is 

 transformed into malate with the release of oxygen. 



We are not far from the actual conditions in which the 

 first reaction of photosynthesis is effected. All the substances 

 taking part in this experimental reaction have been found in 

 the tissues of the higher plants. 



Many other reactions whose place can be predicted in the 

 processes of photosynthesis have been reproduced in the 

 laboratory, particularly by S. Ochoa. The following is another. 



The object is to transform phosphoglycerate into fructose- 

 1-6-phosphate and to couple 2 tricarbonate molecules to give 

 rise to a molecule containing 6 atoms of carbon. It is possible 

 to eff'ect this synthesis by means of chloroplasts illuminated in 



