ix] GLUCOSIDE-SPLITTING ENZYMES 151 



Aesculin is characterized by giving in water solution a blue fluor- 

 escence which can be detected even in great dilution. The fluorescence 

 is increased in alkaline, and decreased in acid, solution. 



Expt. 149. Demonstration of the presence of aesculin in Aesculus bark. Strip off 

 the bark from some young twigs of Aesculus and boil in a little water in an evaporating 

 dish. Filter and pour the nitrate into excels of water in a large veasel. A blue 

 fluorescent solution will be formed. 



GLUCOSIDES OF FLAVONE, FLAVONOL AND ANTHOCYAN PIGMENTS. 

 These substances have already been considered in Chapter vn. 



GLUCOSIDES OF VARIOUS COMPOSITION. 



Coniferin. This glucoside occurs in various members of the Coniferae 

 and also in Asparagus. On hydrolysis with mineral acids or emulsin, it 



breaks up as: 



CH = CHCH 2 OH 



CLJ f\ iLJrt OUI f"> 

 16 n 2'2'-'8 "" n 2^-' ~ ^6 n 12 V -'6 



Coniferin 



\ 



OH 



Coniferyl alcohol 



Arbutin. This glucoside is found in the leaves of the Bearberry 

 (Arctostaphylos Uva-ursi), Pyrola, Vaccinium, and other Ericaceae and 

 also of the Pear (Pyrus communis}. 



On hydrolysis with acids arbutin yields hydroquinone and glucose: 

 C 12 H 16 7 + H 2 = C 6 H 6 2 + C 6 H 12 6 



the same hydrolysis is brought about by the enzyme emulsin. 



It has been suggested that the darkening of leaves of the Pear 

 (Bourquelot and Fichtenholz, 11, 12, 13) either on autolysis or injury, or 

 at the fall of the leaf, is due to the hydrolysis of the arbutin by a gluco- 

 side-splitting enzyme in the leaf, and subsequent oxidation of the 

 hydroquinone so formed by an oxidase. 



Expt. 150. Extraction of arbutin from leaves of the Pear (Pyrus commuuis). 

 Weigh out 100 gms. of fresh leaves (without petioles). Tear the leaves into small 

 pieces and drop them as quickly as possible into about 500 c.c. of boiling 96-98 % 

 alcohol in a flask. Boil for about 20 mins., adding more alcohol if necessary. Then 

 filter off the alcohol and pound up the leaf residue in a mortar and extract again with 



