44 BACTERIOLOGICAL CHEMISTRY 



All enzymes appear to be colloidal when in solution 

 in so far as they are unable to diffuse through semi- 

 permeable membranes, and in showing the T3mdall effect 

 when a beam of light is passed through such a solution. 

 Like the proteins, which in fact many enzymes may be, 

 most of them are amphoteric in nature, that is, they 

 may behave either as weak acids or weak bases depending 

 on the acidity or alkalinity of the medium in which they 

 are dissolved. As a result of their colloidal and amphoteric 

 character enzymes are usually active adsorbing agents, 

 and also display their maximum activity at an optimum 

 2?H value. 



Separation of Enzymes. — The majority of enzymes 

 do not diffuse out of intact cells into the surrounding 

 fluid but are held within the cell structure probably by 

 adsorption to various cell constituents. Hence, in order 

 that they may be isolated, the cell system has to be broken 

 down by mild means in order not to destroy the enzyme 

 at the same time. This may be effected by a mechanical 

 process, such as grinding with sand, as did Buchner when 

 he obtained zjanase from yeast cells, or by such chemical 

 action as the use of weak alkali or acid ; or the cells may 

 be disintegrated by using solvents like ether, chloroform, 

 toluene, or acetone, but these also remove fatty con- 

 stituents. The treated cells may then be extracted with 

 water, salt solutions, dilute acids or alkalies, dilute alcohol, 

 glycerol, or some similar agent, depending on circum- 

 stances. Having obtained a crude enzyme solution in 

 this way, it may be purified in a variety of ways, the 

 appropriate method depending on the particular enzjnne in 

 question. Thus salts, acids and alkalies may be removed 

 by dialysis. The enzjrme may be precipitated from 

 solution, usually along with considerable quantities of 

 inactive protein, b}^ alcohol, acetone, ammonium sulphate, 

 or other protein precipitants . A method which has been 

 particularly valuable in the separation and purification 

 of enzymes, especially in the hands of Willstiitter and his 



