MALTASE 129 



acid for two or three days. The dry mass is then powdered 

 very finely in a mortar and transferred to an air-bath, the 

 temperature of which must be raised very slowly (in about 

 two hours) to 50 C., at which point it must be kept for 

 one hour. 



To demonstrate the presence of maltase in the prepared 

 yeast, add about 0*5 gram of the powder to 100 c.c. of a solution 

 of about 5 per cent, of maltose of known rotatory power 

 containing 0'5 c.c. of toluene as an antiseptic (chloroform 

 must not be used, as it prevents the action of maltase). Cork 

 the flask containing this solution and keep it at a temperature 

 of 35 C. for three or four hours. The solution is then filtered 

 and examined in the polarimeter. A considerable fall in the 

 rotation will be found to have taken place, due to the formation 

 of dextrose ; the presence of dextrose may be confirmed by 

 preparing its osazone. 



The action of maltase upon maltose is of very special 

 interest, as it is the first case of a reversible enzyme action 

 that has been studied. Croft Hill found that if maltase was 

 added to a very concentrated solution of dextrose a disaccha- 

 ride was formed. He at first thought that this was a simple 

 reconversion of dextrose into maltose, but further research 

 showed that the sugar formed was isomeric with maltose. The 

 essential fact remained that while in dilute solutions there was 

 a breaking down of larger into smaller molecules, in concen- 

 trated solutions there was a building up or synthesis of the 

 simpler molecules into more complex. This would seem to 

 indicate that all enzyme actions are potentially reversible, and 

 the direction of the reaction depends on the concentration of 

 the solution and the relative masses of the reacting bodies ; 

 thus in solutions of less than four per cent, of dextrose no 

 formation of disaccharose occurred. 



Subsequent to Croft Hill's researches other instances of 

 reversible enzyme action have been discovered. Thus 

 Fischer and Armstrong have found that isolactose can be 



