GENERAL METABOLISM in vitro 87 



split phosphocreatine even after incubating for 1 hr at 37 °C 

 (Narayanaswami, 1952), suggesting either that a simple hydrolytic 

 enzyme was absent or that it was destroyed or inhibited under the 

 conditions used. With such a dispersion in the presence of adenylic 

 acid or adenosine diphosphate, phosphocreatine was split at a 

 rapid rate presumably by the enzyme creatine phosphokinase. In- 

 organic phosphate accumulated in the medium but the formation 

 of adenosine triphosphate was not measured. In dilute cerebral 

 extracts it was found (Oliver, 1954, 1955) that adenosine diphos- 

 phate was the sole acceptor of phosphate from phosphocreatine, 

 being converted to adenosine triphosphate in the process. Pre- 

 sumably the presence of myokinase in the more concentrated 

 dispersions together with a small quantity of adenosine di- and 

 triphosphates accounts for the results obtained by Narayanaswami 

 (see Ennor and Rosenberg, 1954). The absence of a demonstrable 

 phosphatase carrying out a hydrolytic split of phosphocreatine to 

 phosphate and creatine, together with the demonstration that 

 adenosine triphosphate is the product of creatine phosphokinase 

 action provides good evidence that the initial stage of phos- 

 phocreatine metabolism in brain is the phosphorylation of adenosine 

 diphosphate to adenosine triphosphate. 



Many reactions involving adenosine triphosphate result in the 

 formation of inorganic pyrophosphate and it is of interest that, 

 brain contains a highly active inorganic pyrophosphatase (Gordon, 

 1950 1953; Gore, 1951) liberating inorganic phosphate at rates 

 of up to 2000 jLtmoles/g wet wt. hr~i. The function of this 

 enzyme is not at present known. It is demonstrably different from 

 adenosine triphosphatase, a preparation free from this enzyme 

 having been obtained from swine brain (Seal and Binkley, 1957). 

 The high activity of the enzyme is consistent with the absence of 

 inorganic pyrophosphate in acid extracts of brain. 



The potential degradative activity is thus considerable and in 

 certain instances, for example adenosine triphosphatase, greatly 

 exceeds the possible rate of synthesis. Nevertheless, appreciable 

 quantities of many of the substrates are found in the intact tissues. 

 Considerations of this type have led to views supported by growing 

 evidence, that many enzymes previously considered to function as 

 hydrolases are more probably synthetases. That they are still 

 estimated by means of their degradative capacity is probably a 

 reflection both of the means chosen to demonstrate their presence 



