ENZYMES 51 



only hydrolyse sugars like cellobiose which have p- 

 linkages, or glucosid.es like amygdalin which also have 

 p-glucose bonds. Invertase .attaclvs only sucrose or 

 the trisaccharides, raffinose or gentianose, which contain 

 the same glucose-fructose unit as sucrose. It has not the 

 slightest effect on maltose, cellobiose or lactose. The 

 acids (inorganic catalysts), on the other hand, attack all 

 these sugars at approximately the same rate, and, more- 

 over, they also catalyse other hydrolyses such as the 

 breakdown of protein or of esters and fats with equal 

 facility. The proteolytic enzymes besides being specific 

 as a class also show a certain amount of " internal " 

 specificity, although this is not so sharp. Pepsin and 

 trypsin, for instance, are capable of hydrolysing a whole 

 series of proteins, but the peptidases which attack poly- 

 and lower peptides are much more specific in their action, 

 generally speaking only hydrolysing compounds which 

 have common structures or arrangements of amino-acids. 

 The specificity is often sharp enough to distinguish 

 between optical isomers, one isomer (usually the naturally 

 occurring one) being attacked, while the other is not 

 attacked at all or only very slowly. 



The lipases, or fat -splitting enzymes, while completely 

 specific as a group, that is, capable of hydrolysing only 

 fats and esters, show a relatively low degree of " internal " 

 specificity. Thus any lipase will hydrolyse almost any 

 fat or ester, but there is a certain amount of relative 

 specificity. For example, liver lipase hydrolyses esters 

 readily but fats only slowl}^ whilst the pancreatic lipase 

 behaves conversely, hydrolysing fats readily and esters 

 slowly. 



Enzymes which bring about other types of reaction 

 than hydrolysis are, in general, less specific than the 

 hydrolytic enzymes. They usually catalyse the same 

 type of reaction, oxidation, dehydrogenation, and so on, 

 for a whole range of substrates, which only need to have 



