INTRODUCTION 3 



(AMP), thus forming adenosine triphosphate (ATP) or 

 ADP respectively. 



In a biological system, the only known way in which the 

 energy released by an exergonic reaction can be made 

 available to an endergonic reaction, is for the two reactions 

 to be coupled together by means of a substance which 

 participates in both. This is the function of ATP, which by 

 virtue of its high-energy phosphate groups acts as an energy 

 carrier between reactions yielding energy and those utilizing 

 energy. Adenosine triphosphate participates in the latter by 

 reacting with, and thus activating, one of the reactants, and 

 by this means the total free-energy content of the reactants 

 is raised to a value at least approximately equal to, and often 

 far greater than, that of the products. From the standpoint 

 of energy relationships, the conditions are now such as to 

 favour formation of the products, and the utilization of 

 ATP in this manner is accompanied by the appearance of 

 inorganic orthophosphate. 



Although it is generally accepted that the energy meta- 

 bolism of all organisms is associated with energy-rich 

 phosphate bonds, little is known about how they are formed 

 except during the anaerobic catabolism of glucose and 

 pyruvate. The results of contemporary research indicate 

 that co-factors containing thiol groups probably play an 

 important role both in the production of energy-rich phos- 

 phate groups and in their utilization, and that the synthesis 

 of thiol esters may be an essential intermediate stage in these 

 reactions (cf. the role of glutathione in the triosephosphate 

 dehydrogenase system [16], and coenzyme A (Co. A) in the 

 synthesis of citric acid and other compounds [2]). A sub- 

 stance having the properties of ATP is believed to be present 

 in all organisms and ATP has in fact been isolated from 

 yeast [cf. 4], green plants [i] and animals, but its occurrence 

 in bacteria is based more on inference rather than its isola- 

 tion in a pure state [3, 7, 9, 11, 12, 13, 15]. 



Nutrition: general aspects 



Irrespective of the organism, the continuance of life and 

 the synthesis of cytoplasm are dependent on the availability 



