1904] 



Studies on Enzyme Action. 



505 



although the extract is still very active at 15°, above 38° the activity 

 begins to lessen. The experiments with lactase and emulsin were 

 made at 35 — 37°, those with maltase at about 30°. In making the 

 •experiments, a mixture in the desired proportions of the solution of 

 the sugar and of the enzyme, in a closed flask, was kept at a known 

 temperature in an incubator ; samples were withdrawn from time to 

 time : these were diluted so that they contained 0*2 per cent, of the 

 sugar and their cupric-reducing power was then determined by the 

 modification of Pavy's method described by Croft Hill. A simple 

 ^calculation gave the proportion in which monosaccharide and di- 

 saccharide were present. It may be claimed that the results are 

 comparable ; probably they are affected by an error amounting to 

 at least from 1 to 2 per cent, when the amount of sugar hydrolysed 

 -does not exceed about 70 per cent. 



The proportion or weight of disaccharide hydrolysed during 

 successive intervals having been determined, the results were plotted 

 graphically ; the coefficient of velocity K was also calculated for each, 

 result, on the assumption that the rate of change was proportional to 

 the amount of hydrolyte which undergoes change. 



The actions of lactase and emulsin on milk sugar and of maltase on 



maltose have been studied in the manner described, using solutions 



containing 2, 5 and 10 grammes of the hydrated disaccharide in 



100 c.c. Typical series of results selected from a large number of a 



similar character are quoted in the following tables. In these, t is 



time from the commencement of the experiment, x the percentage of 



substance hydrolysed and K the velocity coefficient calculated from 



Tr 1, 100 

 the equation K =— logio — . 



Lactase. — On contrasting the results given in the two following 

 tables it will at once be obvious that the character of the change is 

 dependent on the proportion which the enzyme present bears to the 

 .sugar. When, as in the case of Experiment I, the proportion of 

 enzyme is relatively large, K falls throughout the whole period of 

 change; whereas, when the proportion of enzyme is considerably 

 reduced, equal amounts of sugar are changed in successive equal 

 intervals of time until about 10 per cent, has been hydrolysed, the 

 value of K increasing at first but afterwards falling rapidly as in the 

 previous case. 



