194 A SYMPOSIUM ON RESPIRATORY ENZYMES 



is easily destroyed, and only the first reaction step of transphos- 

 phorylation, 



(1) P-acceptor + adenosinetriphosphate ±^ P-acceptor — phos- 

 phate + adenosinediphosphate 



is still occurring. A more detailed study of the different enzyme 

 proteins in these phosphorylating reactions along the Hnes suggested 

 by Colowick and Kalckar seems highly desirable. 



M. J. Johnson, University of Wisconsin: 



The present status of our knowledge on biological phosphoryla- 

 tions raises the question whether energy of phosphorylation is the 

 sole form in which energy from food oxidation (or fermentation) is 

 made available for metabolic reactions. In other words, is phos- 

 phorylation the only device employed by the cell to utilize oxidative 

 energy? 



The only answer that can be made at present is that phosphory- 

 lation is the only mechanism we know of by which a part of the 

 energy derivable from the burning of food material can be made 

 available for endergonic life processes. There appears to be no a 

 priori reason to suspect the existence of another mechanism. In fact, 

 the simplicity of a single-mechanism hypothesis seems very attrac- 

 tive. On the other hand, we have no reason to doubt the existence 

 of other "energy-fixing" reactions. The question is entirely open. 



There is, however, at least one fragment of evidence that definitely 

 favors the single-mechanism hypothesis. Yeast growing anaerobically 

 in a simple medium must derive all the energy for its growth reac- 

 tions from the conversion of glucose into ethyl alcohol and carbon 

 dioxide. Unless our present views of the mechanism of this conver- 

 sion are erroneous, no energy-fixing mechanism other than phos- 

 phorylation exists in alcoholic fermentation. Therefore the only form 

 in which energy from the fermentation process is available to the 

 organism is energy of phosphorylation. It follows, of course, that the 

 yeast cell is capable of utilizing, directly or indirectly, energy of 

 phosphorylation for all its metabolic energy requirements. Hence 

 any other energy-fixing reactions which might be postulated to occur 

 during aerobic sugar breakdown are at least not essential for yeast 

 growth. 



