120 EN7A'MES 



action. This curve may be drawn by plotting the differences of 

 the ordinates of (1) and (2) on the same scale of temperatures. 



(c) The hydrogen ion concentration of the medium in which 

 the enzyme acts has nuich to do with its activity. Each enzyme 

 is active only when the bathing fluid has a p^^ of a certain range 

 with an optimum p^^ at which the action proceeds at its best. 

 The extraordinary sensitiveness of colloids to the p^ has been 

 mentioned. 



[d) The crystalloid content of the substrate solution is peculiar 

 for each enzyme. Certain salts are, of course, destructive. All 

 salts which break up colloidal complexes, inhibit or destroy 

 enzyme action. Enzymes are " salted out " by the neutral salts 

 that precipitate colloids and may thus be separated. 



{e) Anaesthetics have no effect on enzyme action. 



Chloroform, thymol, etc., may therefore be used to keep experi- 

 mental enzyme solutions free from bacteria. 



To sum up, — the ranges of temperature, p^, salt content, etc., 

 all point to the colloidal nature of enzymes. 



The material on which an enzyme acts is called its substrate, 

 and each enzyme acts on a specific substrate and on no other. In 

 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 

 proteinase I 



protease j " 



aldehydase ,, aldehyde 



lipase ,, lipides 



peroxidase ,, peroxide 



arginase ,, arginine 



urease ,, urea. 



Sometimes the function of the enzyme may be indicated by 

 its name, viz. : 



oxidase accelerates oxidation (= peroxide + peroxidase) 

 catalase ,, breaking down of peroxides 



invertase ,, inversion of cane sugar 



desamidase ,, removal of amino groups. 



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 ((ir. Pepsis — digestion) = acid or gastric proteinase. 



protein 



