46o ENZYMES 



(d) Protein-splitting enzymes : — 



Protease, which hydrolyses proteins to albuminoses and peptones. 

 Peptidase ,, ,, albuminoses, peptones and other poly- 



(erepsin) peptides to amino acids. 



Amidase ,, ,, amino compounds to ammonia. 



(e) Urea-splitting enzymes :• — 



Ureases, which hydrolyse urea into ammonia and carbon dioxide. 



2. Fermenting Enzymes. 



Alcoholic fermentation of glucose, fructose, mannose, etc., by zymase. 

 Lactic acid fermentation of lactose by lactic acid bacteria. 

 Butyric acid fermentation of lactose by the butyric bacteria, etc. 



Coagulating Enzymes. 

 Rennin (Chymosin), which curdles milk. 

 Thrombin which coagulates blood. 

 Pectase ,, ,, soluble pectic bodies. 



4. Oxidising Enzymes. 



Oxidases which oxidize phenols and chromogens. 



Oxygenase, which oxidizes catechol with the formation of a peroxide. 



Peroxidase, which sets free active, or atomic, oxygen from hydrogen 



peroxide, or other peroxides. 

 Catalase, which splits molecular oxygen from hydrogen peroxide only. 



ISOLATION AND PURIFICATION OF ENZYMES. 



To obtain an active enzyme from a given source, the 

 material is thoroughly ground in water, dilute alcohol or 

 glycerol, sand being added, if needs be, to break up the 

 cell wall. The filtrate can be used in qualitative work and to 

 it antiseptics may be added if the experiment be protracted. 

 The antiseptics commonly used are chloroform, toluene, 

 tri-cresol, thymol, or sodium fluoride. 



The solution obtained as above is a crude preparation. 

 If it is likely to contain crystalloids, these may be removed 

 by dialysis. By pouring the solution into absolute alcohol 

 the enzyme is precipitated ; the precipitate is filtered off, 

 dissolved in water and again precipitated with alcohol. The 

 enzyme is filtered off and dried in a vacuum desiccator. The 

 preparation will still be impure, being contaminated with 

 protein and other substances. 



Enzymes are colloidal substances which exhibit in a marked 

 degree the phenomenon of adsorption, as a result of which 

 they tend to be removed from solution by adsorption on any 

 precipitate formed in their presence or by the addition to 

 their solutions of substances presenting a large surface such 

 as animal charcoal. Making use of these facts, Willstatter 



