ENZYMES 49 



if all the mineral constituents of the enzyme preparation 

 and of the starch are removed by dialysis no hydrolysis 

 will occur when the solutions are mixed, but immediately 

 a certain amount of sodium chloride is added to the 

 mixture breakdo^\Ti of the starch commences. Many 

 oxidation enzymes, or oxidases, require manganese ions 

 as activator. Trypsin, as it is obtained from the pancreas, 

 will only hydrolyse the partially degraded proteins, 

 protamines and peptones ; in order that it may attack 

 the complex parent proteins it must be activated by 

 another enzyme, entero kinase, which is to be found in the 

 intestinal juice . Enterokinase probably owes its activating 

 effect to the conversion of the pro-enzjmie, tripsinogen, 

 into trypsin. A number of activators, for example, the 

 heat stable co -enzyme in yeast juice (about which we 

 shall say more when we deal with alcoholic fermentation) 

 function by forming an essential link in a chain of re- 

 actions (see p. 267). 



(/) Inhibition. — Many heavy metals have the power 

 of inhibiting enzyme activity. Thus mercury salts 

 " paralyse " the hydrolysis of sucrose by invertase, and 

 barium salts inhibit the breakdown of urea by urease. 

 This action is probably the result of the adsorption of 

 the metal on to the enzyme with a consequent blocldng 

 of the adsorption of the substrate. Removal of the 

 metal by dialysis, for instance, or by appropriate chemical 

 means restores the activity of the enzyme, no permanent 

 harm having been done to it. Anaesthetics like chloro- 

 form and urethane inhibit dehydrogenase activity, whilst 

 cyanides, carbon monoxide and sulphides inhibit oxidases, 

 a fact which has had an important bearing in the sorting 

 out of respiratory mechanisms. Certain organic bases, 

 such as amines, will inhibit the action of invertase, but 

 their effect can be annulled by the action of aldehydes . 



It is possible that a closer study of the inhibiting 

 action of compounds or chemical groups on different 

 types of enz^Tnes may throw considerable light on the 



