348 ENZYMES 



other hand, the peel does. The peel is actively proteolytic, 

 but not the pulp and juice. Similarly the latex of the fig, 

 papaw, lettuce, and spurge, has proteolytic qualities and also 

 gives the peroxidase reaction. The meaning of this associa- 

 tion is not clear. 



CLASSIFICATION OF ENZYMES. 



The following classification of enzymes, based on the 

 chemical reactions in which they exert their accelerating 

 influence, indicates the extensive use made by nature of these 

 catalysts : — 



I. Hydrolytic Enzymes. 



(a) Ester or fat-splitting enzymes (esterases) : Lipase. 

 {b) Carbohydrate-splitting enzymes (carbohydrases) : — 



Invertase which hydrolyses cane sugar to dextrose and levulose. 



,, ,, ,, raffinose to levulose and melibiose. 



Maltase „ ,, maltose (malt-sugar) to dextrose. 



Lactase ,, ,, lactose (milk-sugar) to dextrose and 



galactose. 

 Amylase or Diastase which hydrolyses starch to maltose and 



dextrin. 

 Inulase which hydrolyses inulin to levulose. 

 Pectinase* which hydrolyses pectose to arabinose. 

 Cytase which hydrolyses hemicellulose to mannose and galactose. 

 (c) Glucoside-splitting enzymes : — 



Emulsin which hydrolyses amygdalin to glucose, hydrocyanic 

 acid and benzaldehyde. 

 „ „ ,, /8-methylglucoside to glucose and 



methyl alcohol. 

 Myrosin „ ., potassium myronate to allylisothio- 



cyanate, glucose and potassium 

 hydrogen sulphate. 

 Phytase „ ,, phytin to inosite and phosphoric acid. 



{d) Protein-splitting enzymes : — 



Pepsin contained in the stomach which hydrolyses proteins to 



albumoses and peptones. 

 Trypsin ,, ,, pancreas which hydrolyses proteins to poly- 



peptides and amino-acids. 

 Erepsin ,, ,, intestine which hydrolyses proteins to poly- 



peptides and amino-acids. 

 Bromelin ,, ,, pine-apple juice which hydrolyses proteins to 



polypeptides and amino-acids. 

 Papain , ,, juice of the fruit and leaves of the papaw 



tree (Carica papaya) which hydrolyses 

 proteins to polypeptides and amino-acids. 

 (e) Urea-splitting enzymes (ureases) : — 



Ureases obtained from Micrococcus urece and also from the Soja 

 bean and other seeds f which hydrolyse urea into ammonia and 

 carbon dioxide. 



* See p. i2g. 



f Annett : " Biochem. Journ.," 1914, 8, 449, 



