1904.] 



Studies on Enzyme Action. 



523 



In proof of this contention the following facts may be adduced : — 

 It is to be remembered that each hexose can give rise to two 

 stereoisomers hexosides (e.g., a- and /3-methyl glucoside), which differ 

 only in the fact that the RO group and an atom of hydrogen are 

 attached to the carbon atom in different relative positions : nevertheless, 

 these require different enzymes to effect their hydrolysis. It is 

 obvious, therefore, that but a slight shifting of the one radicle in space 

 is sufficient to throw the enzyme out of action. 



Yet it would seem that the enzyme is only out of harmony with the 

 glucoside at the terminal point, inasmuch as the action of emulsin on 

 milk sugar is hindered not only by glucose but also, although to a less 

 extent, by a-methyl glucoside, which is not in the least attacked by 

 emulsin, whereas the corresponding /3-glucoside is readily hydrolysed. 



Time in 10 grammes milk sugar + 10 grammes 



hours. per 100 c.c. a-niethyl glucoside. 



3 11*2 8-3 



6 15-2 12-1 



25 32-7 24-5 



[Note added May 30, 1904. — Since this paper was presented a series 

 of observations have been made with glucosides. A second experiment 

 with the a-glucoside confirms the results arrived at in the first. 



Time in 10 grammes milk sugar + 10 grammes 



hours. per 100 c.c. a-methyl glucoside. 



5 7-9 5-7 



23 23-3 16-9 



28 27-1 19-0 



In a similar manner, a-methyl galactoside, which is itself unaffected 

 by the enzyme, hinders the hydrolysis of milk sugar by lactase practi- 

 cally to the same extent as galactose itself does. 



Time in 10 grammes milk sugar 4 10 grammes + 10 grammes 



hours. per 100 c.c. a-methyl galactoside. galactose. 



2 7-9 5-3 4-8 



5 14-9 9-7 9-6 



26 27-8 20-2 20'0 



On the other hand a-methyl glucoside like glucose has no retarding 

 influence on the hydrolysis of milk sugar by lactase. 



Lastly, /3-methyl glucoside was found to retard the action on maltose 

 of maltase, which easily hydrolyses the a-glucoside though it is entirely 

 without action on the /3-glucoside. 



