PREPARATION 461 



has developed a technique of adsorption on kaolin, alumina, 

 lead phosphate, and other substances, whereby not only may 

 enzymes be largely separated from ordinary impurities but 

 also from their activators.* In general terms, the smaller 

 amount of adsorbent required, the higher is the degree of 

 purity attained. The adsorbed enzyme is removed from 

 its adsorbate by such gentle chemical means as dilute alkali, 

 alkaline phosphate, or weak acid according to the relation 

 between the enzyme and its adsorbate, which relationship 

 cannot be foretold. 



The adsorption is influenced by various factors, the chief 

 of which are as follows :— 



1. The nature of the solvent in which the enzyme is dis- 

 solved ; peroxidase, for example, is not adsorbed from an 

 aqueous solution, but is from an alcoholic solution. Likewise 

 papain is better adsorbed from an alcoholic solution. 



2. The reaction of the medium is not without influence : 

 papain, for example, is but feebly adsorbed from an acid 

 solution, better from a neutral solution, and best from a 

 feebly alkaline solution. It is freed from its adsorbent by 

 a weak acid. 



3. Concentration. In certain instances, e.g. saccharase, 

 the use of a very dilute solution results in a preparation of 

 greater purity. 



4. The nature of the adsorbent on which depends the 

 degree of selectivity. Its significance may be illustrated by 

 the use of various preparations of aluminium hydroxide in 

 the gel state. t Autolysed yeast contains maltase and sac- 

 charase ; these may be separated by the use of jS-alumina, 

 A1(0H)3, or of metahydroxide of alumina, AlOgH, both of 

 which adsorb maltase readily and saccharase very sparingly. 

 The maltase may be recovered by treatment with alkaline 

 phosphate. 



* See Willstatter : " J. Chem. Soc," 1927, 1359. 



t Aluminium hydroxide is precipitated in the form of a gel from 

 aluminium salts. It first comes down in the form of an unstable gel, 

 Al(OH)3, which is termed a ; a changes quickly into a j3 variety, which 

 changes slowly into a stable variety, termed y. By heating yAl(OH)3 with 

 ammonia to 250° C, a gelatinous hydroxide of the formula AlO^H is 

 obtained. 



