96 ENZYMES 



many cases the name applied to the enzyme is derived from that 

 of its substrate by altering the terminal syllable to ase. Thus 

 maltase acts on maltose. 



Lactase acts on lactose 



protease protein 



aldehydase ,, aldehyde i 



lipase ,, lipin 



peroxidase ,, peroxide. 



Sometimes the function of the enzyme may be indicated by 

 its name, viz. : 



oxidase oxidises ( =peroxide +peroxidase) 



catalase breaks down peroxides 

 invertase inverts cane sugar. 



The majority of enzymes of physiological importance, however, 

 have no accepted systematic name. They are the ones first 

 known and they were named to suit the fancy of their discoverer. 

 Ptyalin (Gr. Pteuin to spit) acts on starch and should be called 

 salivary amylase. Several others are in a similar position, e.g. 

 Pepsin (Gr. Pepsis digestion) =acid or gastric protease. Trypsin 

 (Gr. Tribein to rub prepared by rubbing pancreas with sand 

 and glycerol) =alkaline or pancreatic protease. 



Some writers prefer to use names which point to the splitting 

 power of the enzymes, e.g. 



proteolytic or proteoclastic enzymes act on proteins 

 amylolytic or amyloclastic ,, ,, starches 



lipolytic or lipoclastic ,, ,, fats. 



On the other hand, hydrolytic enzymes produce their effect by 

 adding or subtracting water. 



Some enzymes act in the cells while others are secreted by the 

 cells and act on a substrate outside the cell. The former, endo- 

 enzymes, have been little studied. An active suspension of them 

 may be prepared by grinding up tissue with sand and extracting 

 with watery glycerol. It is probable that all muscle cells contain 

 enzymes which act on protein disintegration products, either 

 rebuilding proteins from amino acids or breaking down these 

 amino acids. Similarly ; the regeneration and the disintegration 

 of carbohydrates and fats have been attributed to endo-enzymes. 

 There are also special enzymes to carry out oxidations and re- 

 ductions in the cell. The various stages in the production of 

 uric acid from nucleoprotein have been studied exhaustively, and 

 each stage has been shown to have its enzyme or series of enzymes. 



