452 PROTEINS 



the fact that the production of amyl alcohol or fusel oil by 

 the yeast fermentation of sugar has always been a source of 

 trouble to spirit distillers, necessitating elaborate processes 

 for refining.* 



Since, moreover, other amino acids besides the leucines are 

 also found to be attacked in a similar way with the production 

 of a number of widely different products, some of which are 

 aromatic, it is easy to account for the different flavours which 

 are peculiar to the various alcoholic beverages, all of which 

 are ultimately produced by alcoholic fermentation of sugars in 

 presence of different proteins. 



The destruction of amino acids by enzymes derived from 

 yeasts, fungi or bacteria with the formation of different bye- 

 products, may also account for the flavours of different 

 cheeses, as well as the odour of flowers ; the substance phenyl 

 ethyl alcohol, for example, which is produced by the fer- 

 mentation of phenyl alanine — 



CsHsCHaCHNHXOOH + H^O = CsHjCHaCHaOH + CO^ + NH3 

 Phenyl alanine Phenyl ethyl alcohol 



being the chief odoriferous constituent of rose oil. 



These researches would therefore lead to the conclusion 

 that the proteins, through the breaking up of various amino 

 acids derived from them, are ultimately responsible for the 

 production of a variety of nitrogen-free alcohols, aldehydes 

 and acids as bye-products, which go to produce the different 

 essential oils, etc. 



The metabolism .of proteins in the animal world is, as is 

 well known, a very important process and results in their very 

 complete decomposition with the formation of urea, carbon 

 dioxide and water. Although little is known concerning the 

 metabolism of proteins by plants, there is good reason for be- 

 lieving that the destruction of the protein molecule is far less 

 complete ; the occurrence of urea has in fact been recorded in 

 small quantities in higher plants, namely, Cichorium endiva, 

 Cucurbit a maxima, Cucumis melo, Br as sic a olereacea, B. nigra 



* Amyl alcohol is required for the preparation of amyl acetate, used 

 as a flavouring material for confectionery, and as a solvent in the manu- 

 facture of varnish, smokeless powder, etc. 



