1913.] Processes Operative in Solutions and Enzyme Action. b77 



alkalinity of any solution is always unity. He proposes the use of a series of 

 standardised solutions of the two phosphates KH2PO4 (acid) and Na 2 HP04 

 (alkaline) in certain proportions. The relative acidity and alkalinity of such 

 mixtures being known, it is easy to determine that of any given solution by 

 matching the tint which it produces when mixed with azolitmin with that 

 produced by one of the mixtures. The values given by N/15 solutions vary 

 between a relative acidity of 300 and a relatively alkalinity of 20. Inasmuch 

 as most enzymes show maximum activity within this range, such solutions 

 afford very convenient standards. As illustrating the delicacy of the control, 

 it may be added that whereas the relative acidity of a solution of N/15 acid 

 phosphate is 300, that of N/10 acetic acid is 13,000. 



In the past we have emphasised the need of carefully excluding all alkaline 

 impurity in studying the action of saccharoclastic enzymes and have shown 

 that the addition either of faintly acid or of amphoteric substances such as 

 glycine was of material advantage in the case of invertase. Other workers 

 have since used an acid phosphate for the same reason. 



The method we have adopted in the experiments now to be referred to has 

 been to extract dried yeast powder with the phosphate solution and after 

 filtration to add a certain portion — about 20 c.c. — of the extract to a solution 

 of a-methyl glucoside in 80 c.c. of the same phosphate mixture. The acidity 

 of such a mixture is approximately, though not strictly, that of the original 

 phosphate. On account of the yellow colour of the solution, it is impossible 

 to determine the acidity exactly by the colorimetric method practised by 

 Sorensen nor were we concerned to achieve such a degree of accuracy : for our 

 purpose, it was sufficient to know that the solutions used varied in acidity. 



As might be expected, an extract of dried yeast contains sufficient soluble 

 material to provide a highly favourable medium. Thus, a solution made 

 with ordinary distilled water containing carbon dioxide had a relative activity 

 of 83 towards «-methyl glucoside ; when distilled water free from dissolved 

 carbon dioxide was used, the slightly lower value 75 was obtained ; when a 

 mixture of acid and alkaline phosphate in the proportions necessary to give 

 neutrality was used the relative activity of the extract was 84. 



The great variation in the results obtained with solutions of various degrees 

 of acidity and alkalinity is well shown in the table on p. 578. 



In the experiments lasting four hours, the activity was clearly at a 

 maximum in faintly acid solutions. 



The maximum is less marked in the case of the experiments lasting 

 21 hours. The limits within which action takes place are obviously very 

 narrow. 



2 u 2 



