82 ENZYMES AND DRUG ACTION 



The Action of Drugs on Respiration and 

 Glycolysis in Muscle 



From the evidence which can be derived from studies on 

 living cells it is clear, as we have just seen, that there 

 are great difficulties in analysing the action of a drug 

 into terms of activities on specific enzyme systems. An 

 alternative approach to the problem can be made by 

 studying the enzyme systems involved in a particular 

 physiological process on the test-tube scale, i.e. using tis- 

 sue extracts. This procedure has been carried out in great 

 detail in the case of the respiration and glycolysis of 

 muscle. The results so obtained seem likely to be repre- 

 sentative of the type of conclusion which will be reached 

 when a completely satisfactory analysis of drug actions 

 on enzymes is available. At present we must have some 

 reservations about the theories put forward by the bio- 

 chemists, because the enzyme systems have in most 

 cases been shown to perform the functions ascribed to 

 them in vitro only. In the case of the cytochrome system, 

 Keilin and others have provided direct evidence that 

 the intracellular systems are behaving in the way which 

 is postulated from test tube experiments. But so far as 

 glycolysis is concerned, whilst the picture built up by 

 biochemical studies is very plausible, we still await con- 

 clusive evidence from studies on living tissues that the 

 chain of events is identical with that postulated. 



With these, and certain other reservations which will 



