122 



Prof. Keeble, Dr. Armstrong, and Mr. Jones. 



This conversion of a glucoside into substances which simulate both the 

 colour and odour of ripe fruit is noteworthy, and suggests that in the natural 

 process of ripening of fruits, not only are glucosides hydrolysed and certain 

 of their products oxidised by oxydases, but also that amino-compounds, so 

 common in plants, intervene in the reaction and determine the nature of the 

 end products. 



The reaction between quinone and the products of oxidation of the amino- 

 acids is obviously very complicated, and we therefore content ourselves with 

 a reference to two somewhat similar cases which have been emphasised as of 

 biological importance : — 



1. Strecker and Hurtley and Wooton have shown that by the interaction 



of glycine and alloxan, CO<^-g-'£,Q>C(OH) 2 , at the ordinary tempera- 

 ture, the amino-acid is oxidised to formaldehyde, carbon dioxide, and 

 ammonia, whereas the alloxan is in part reduced to dialuric acid. The 

 unchanged alloxan and dialuric acid combine to produce alloxan tin, which 

 with the ammonia forms murexide (ammonium purpurate). This substance 

 has a characteristic purple colour. On warming the mixture, secondary 

 changes take place with the formation of other coloured products, and in the 

 case of tyrosine Hurtley and Wooton note that a " flowery " odour is produced. 



2. Euhemann has shown that triketohydrindene hydrate, 



C 6 H 4 <£°>C(OH) 2 , 



which gives a deep blue coloration with amino- acids, behaves like alloxan. 

 The hydrindene is now regarded as a valuable reagent for amino-acids, and 

 it has already been of service in investigating problems of animal physiology. 

 In this case also the amino-acid is oxidised to carbon dioxide, ammonia, and 

 aldehyde, and the triketohydrindene is reduced. Hydrindanthin is produced 

 and interacts with ammonia to form the blue ammonium salt of diketo- 



CO CO 



hydrindyhdene-diketohydrindamine, C 6 H4< ( -,q>CH.N:C<£q>C 6 H 4 , which 

 is an analogue of murexide. 



It is probable that similar changes take place in the case of quinone and 

 amino-acids. Starting from arbutin, where the hydroquinone which is formed 

 is oxidised in part to quinone, it is the ammonia from the amino-acid which 

 is the essential factor in producing the red colour. The aldehyde derived 

 from the amino-acid plays only an accessory part, for the reduced quinone is 

 already present. In fact, the red is instantly produced when ammonia is 

 added to the oxidised mixture. The addition of formaldehyde to hydrolysed 

 and oxidised arbutin has no effect in producing colour, and this is in agree- 



