478 ENZYMES 



ISOLATION OF DIASTASE. 



Diastase commonly is prepared from malted barley which 

 yields in addition to amylase, the polysaccharide-splitting 

 enzymes lichenase and mannanase, together with the disac- 

 charide-splitting enzymes cellobiase, mannobiase, etc.* 

 Lintner's f method may be used. One part of malt is ex- 

 tracted with 2-4 parts of 20 per cent alcohol for twenty- 

 four hours. The solution is filtered and to the filtrate is 

 added 2-3 times its volume of absolute alcohol. The pre- 

 cipitated enzyme is filtered off, washed with ether, and dried 

 in vacuo. A certain degree of purification is effected by dis- 

 solving in water, dialysing and reprecipitation with alcohol. 



The optimal temperature of amylase is 40-56° C. ; it varies 

 according to the source and the amount of impurities. The 

 optimal reaction of plant amylases in general is P^ 5 0-5 -4, 

 that of malt amylase is P^ 4-3-4-5. 



QUANTITATIVE DETERMINATION OF THE ACTIVITY OF 



DIASTASE. 



The diastatic value of malt extract may be determined by 

 the method of Lintner as follows : 25 grams of malted barley 

 are ground and mixed with 500 c.c. of water and kept at room 

 temperature for six hours, after which period the extract is 

 filtered. Into a series of ten test tubes are delivered o-l, 0-2, 

 0-3 ... I c.c. of the filtered extract, and then to each tube 

 are added 10 c.c. of 2 per cent soluble starch. The tubes are 

 shaken up and kept at 21° C. for one hour, at the expiration of 

 which 5 c.c. of Fehling solution are added to each. The tubes 

 are then placed in a boiling water bath for ten minutes. The 

 tube which contains the least amount of enzyme and in which 

 the copper salt is completely reduced is then selected. 

 The diastatic power is calculated on the assumption that, 

 under these conditions, o-i c.c of malt extract produces just 

 enough sugar to reduce completely 5 c.c. Fehling solution, 

 and this diastatic value is taken as 100. From this it follows, 

 from proportion, that if the second tube which contained 0-2 c.c. 



* Pringsheim, Genin, and Perewosky : " Biochem. Zeit.," 19^5. 164, 117. 

 t Lintner : " Zeit. Brau.," 1908, II., 32, 421. 



