40 BACTERIOLOGICAL CHEMISTRY 



Since catalysts and enzymes do not, in general, affect 

 the equilibrium of a reversible reaction they should be 

 able to bring about the formation of, say, an ester from 

 the constituent acid and alcohol as well as influence the 

 hydrolysis of the ester. This is found in practice to be 

 the case. For instance, lipase hydrolyses esters, such 

 as ethyl butyrate, with production of the alcohol and 

 the acid, but if it is allowed to react with a mixture 

 of ethyl alcohol and butyric acid it will catalyse the 

 production of the ester. Similarly the disaccharides 

 maltose and cellobiose have been obtained by the action 

 of maltase and emulsin respectively on glucose solutions ; 

 but the yields of disaccharide are very low, as the equi- 

 librium state is far over on the side of hydrolysis. Poly- 

 peptides have also been built up by the action of pepsin 

 on mixtures of peptides. 



The Chemical Nature of Enzymes. — The chemical 

 nature of most enzymes is still a mystery. They are all 

 regarded as proteins, or as being protein like, although 

 for a time there was doubt about some of them, such as 

 invertase, peroxidase and lipase, which were very highly 

 purified by Willstatter and his colleagues and then failed 

 to exhibit the biuret, Millon and ninhydrin reactions 

 typical of proteins, although possessing 500 to 20,000 

 times the activity of the original crude preparations. 

 This failure is very probably due to the fact that the 

 enzyme solutions contained so little of the very highly 

 active enzyme that positive chemical reactions could not 

 be elicited. It may be noted that, generally, these highly 

 purified enzymes are considerably less stable than cruder 

 preparations, in which the impurities seem to have a 

 protective effect. All the crystalline enzymes which 

 have been prepared, listed in Table 2, are either protein 

 in character or contain a protein fraction combined with 

 a prosthetic group. 



