METABOLISM IN THE NORMAL FUNCTIONAL STATE 11 



glucose 1 : 6-diphosphate, the coenzyme of phosphoglucomutase, 

 though apparently low, is actually three times the amount found in 

 liver. The quantity of an intermediate accumulating at any given 

 time is governed as much by its rate of removal as by its rate of 

 synthesis. The apparent absence, or small quantities, of many 

 phosphates known to be produced during metabolism is therefore 

 not necessarily an indication of the unimportance of such meta- 

 bolites or of the routes on which they occur. 



Phosphates other than those listed in the above tables include 

 glycerylphosphorylethanolamine isolated from cattle brain (Walker, 

 1952) and rat brain (Ansell and Norman, 1953) and propanediol 

 phosphate from cow brain (Lindberg, 1946). A fraction considered 

 to be a choline ester of sphingosine phosphoric acid was obtained 

 from extracts of sheep and horse brain (Booth, 1953) and later from 

 dog brain (Stone, 1943), but the existence of this as a major com- 

 ponent of such extracts is doubtful (Dawson, 1958). 



Consideration of the data given above clearly indicates that the 

 major interest has so far largely been centred on adenosine di- and 

 triphosphates, phosphocreatine and inorganic phosphate. This is 

 understandable largely because they were discovered earlier, but 

 also owing to the interest arising when the demonstration of 

 the role of phosphocreatine in muscular activity (Eggleton and 

 Eggleton, 1927; Davenport and Sacks, 1929; Lundsgaard, 1930, 

 1931) was followed by the description of a similar relation for 

 phosphocreatine in peripheral nerve (Gerard, 1932). However 

 phosphocreatine was not identified in brain until 1935 (Kerr, 1935) 

 nor was the presence of adenosine triphosphate unequivocally 

 demonstrated until 1941 (Kerr, 1941). The elaboration of a 

 system of analysis for the acid-soluble phosphates of brain by 

 Stone (1940, 1943) and its application to cerebral tissues subjected 

 to different treatments in vivo, revealed that in brain, as in muscle, 

 changes in function could be related to changes in the quantities of 

 these phosphates. For these reasons the major part of the work in 

 vivo has been concerned with the amounts of such phosphates 

 present under a wide variety of changed conditions. 



Acid-insoluble Phosphates 



After removal of materials soluble in acid denaturants the 

 residue consists of a mixture of phosphorus compounds collec- 

 tively known as ''the acid-insoluble phosphates". The greater 



