416 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



THE MEASUREMENT OF THE ACTIVITY OF 

 ENZYMES. 



In order to determine the activity of an enzyme solution four 

 factors must be taken into account. This was first clearly established 

 by Kjeldahl in 1879 in the case of the diastatic enzyme of malt, 

 namely : 



(1) The temperature at which the action takes place. 



(2) The time during which the enzyme acts. 



(3) The amount of enzyme solution. 



(4) The concentration of the substrate solution. 



The amount of enzyme solution must be small in comparison with 

 the amount of substrate and the change must not exceed 30-40 per 

 cent, of the total change. These statements correspond to the curve 

 of the catalytic action of enzymes. The curve is linear at the com- 

 mencement and again at the end. The measurement is proportional 

 only during the linear part of the curve where the amount of enzyme 

 is small and the substrate large in comparison. The linear portion of 

 the curve corresponds to 30-40 per cent, of hydrolysis. 



The temperature and the concentration of the substrate are fixed, 

 and by fixing either the time or the amount of enzyme solution the 

 fourth factor can be determined. As the basis of comparison it is 

 best to determine the time taken to effect an equal change. This is 

 most important where the reaction takes place in stages ; comparable 

 values can be obtained only in this way. More frequently the 

 amount of enzyme required to produce an equal change, or the 

 amount of change produced by equal amounts of enzyme solution in 

 a given time, is determined. 



The measurements are made either by chemical methods or by 

 physical methods, depending upon the properties of the substrate and 

 the products. 



L Diastase. 



The measurement of the diastatic activity of malt is of practical importance 

 in brewing and certain standard methods of making the extract and of de- 

 termining the hydrolysis have been adopted. 



Preparation of the Extract. 



25 gm. of malt are treated with 500 c.c. of water for 3 hours at 21. 

 The solution is filtered and the first 100 c.c. are rejected. The activity of 

 the perfectly clear extract is determined by method (a) or (b). 



