120 



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



We now find that if a mixture of arbutin and glycine be hydrolysed by 

 emulsin and then oxidised by means of the oxydase present in an aqueous 

 solution of bran, an intense red coloration is produced. The red substance 

 is evidently derived from the interaction of ^-quinone with glycine, or its 

 oxidation products formaldehyde and ammonia. A similar red colour is 

 obtained when, instead of glycine, alanine, leucine, phenylalanine, tyrosine, 

 or asparagine is used. The colour is also produced when arbutin is incubated 

 at 37° with a little ground sweet almond and a drop of hydrogen peroxide. 

 The almond contains emulsin, peroxydase and amino-acids, so that it allows 

 of the whole series of changes. 



The changes may be represented schematically as follows : — 



Emulsin. 



Arbutin + water — a- quinol + glucose. 

 Oxydase. 



Quinol + oxygen — ^ quinone. 



Oxydase. 



Glycine 4- oxygen — s- formaldehyde, ammonia, and carbon dioxide. 

 Quinol + quinone + NH 3 = red compound. 



The production of a red colour from quinone and amino-acids was first 

 observed by Wurster* and later by Kaciborskif but neither author offers 

 any explanation of the phenomenon. The reaction has been studied recently 

 by E. A. Cooper,^ who holds that the colour results from the interaction of 

 the — NH 2 groups of the amino-acid and the oxygen atoms of the quinone, 

 and that the reaction is similar to that which takes place between an amine, 

 such as aniline, and quinone. In the latter case the aniline residues may 

 enter the ring in the 1, 3 positions, or, in addition, form an anil or dianil by 

 replacing the quinone oxygen. 



OOO NC fi H s 

 /\ C fi H=NH /\ NHC 6 H= /\ 



\/ \/ \/ \y 



O O NC 6 H 5 NC 6 H S 



Quinone. Dianilinoquinone. Quinone anil. Quinone dianil. 



The abnormal behaviour of the amino-acids, under conditions when other 

 compounds containing a primary amino-group form condensation products, 

 was shown originally by Strecker.§ He proved that alloxan oxidises alanine 



* ' Chem. Zentr.,' 1889, vol. 1, p. 392. . 

 t ' Chem. Zentr.,' 1907, vol. 1, p. 1595. 

 I ' Biochem. Journ.,' 1913, vol. 7, p. 186. 

 § ' Annalen,' 1863, vol. 123, p. 363. 



