54 EXTRACTION OF ENZYMES 



enzymes. The material should always be ground to a fine 

 powder, from which an extract is made, usually with cold water ; 

 if the filtered solution is at all bulky, it will be convenient to 

 reduce its volume bv evaporation at a temperature not exceeding 

 50° C. The solution is treated with an excess of alcohol and 

 the resulting precipitate allowed to settle. It is then filtered 

 off, redissolved in distilled water, and can be purified by a further 

 precipitation with alcohol. 



A solution of invertase which will invert cane-sugar is readily 

 obtained, according to Plimmer.i in the following manner. A 

 quantity (100 grams) of ordhiary Yeast is ground up with about 

 6 grams of calcium carbonate. The resulting paste is treated 

 with 5 c.c. of chloroform or ether (to kill the Yeast cells), and 

 allowed to stand exposed to the air for three or four days, after 

 which the enzyme is precipitated from the filtrate with an equal 

 volume of alcohol. An impure solution of invertase, which will 

 demonstrate the inversion of cane-sugar, can, howc^'er, be 

 obtained by simply mashing Yeast in water with the addition of 

 a little ether, and filtering oif the sohd matter (preferably through 

 an asbestos filter). 



Lipase can be prepared from the seeds of the Castor Oil by 

 cutting up the endosperm into small pieces, and soaking these 

 for a short time in a small quantity of ether in order to remove 

 the oil. The material is then ground into a pulp with a very 

 dilute (o'5 per cent.) solution of acetic acid, which sets free the 

 enzyme. The insoluble matter is filtered oft\ washed till the 

 filtrate gives no acid reaction, and the residue is shaken up with 

 a small amount of water. If some of this suspension be added 

 to a little ohA'e oil, an acid reaction will soon be obtained due 

 to the formation of fatty acids consequent upon the decom- 

 position of the oil. 



The preparation of proteolj-fic enzymes from plant-material 

 is a matter of some difficulty and beyond the scope of this book. 

 The action of such ferments is, ho\ve\'er, ^\•ell illustrated by the 

 use of peptonising powders (containing the enzMiie pepsin) in 

 rendering milk more digestible for nn-alids. 



The action of enzymes is \-ery often a h\'drol)'tic one, that 



1 Praclical Oi'i;aiiic and Bioclicniislry, p. 31)9. 



