vii] OXIDIZING ENZYMES 107 



Expt. 111. Formation of allocyanin and allocyanidin from plant extracts. For this 

 purpose the yellow varieties "Primrose" or "Cloth of Gold" of the Wallflower 

 (Cheiranthus Cheiri) can be used. The flowers are pounded in a mortar, extracted 

 with cold water, the water extract acidified with sulphuric acid, and zinc dust (or 

 mercury and magnesium powder as above) added. A red coloration is slowly 

 developed. To some of the red solution add aruyl alcohol. The colour is not 

 abstracted (allocyanin). Boil another portion. The allocyanin is thus converted into 

 allocyanidin which is then taken up on addition of amyl alcohol. 



THE OXIDIZING ENZYMES. 



There is a certain group of enzymes of which we have most informa- 

 tion in their connexion with aromatic substances. These are the oxi- 

 dizing enzymes. 



The presence of such enzymes in plants was long 'ago associated with 

 the following phenomena. If the expressed juices, or water extracts of 

 the tissues, of some plants are added to a solution of guaiacum gum, in 

 the presence of air, a deep blue colour is obtained in a short time. On 

 the other hand, expressed juices, or water extracts, of other plants added 

 to guaiacum solution produce no blue colour. On addition, however, of 

 a few drops of hydrogen peroxide, in the latter case, the blue colour 

 rapidly develops. Plants are said to contain an oxidase when the extracts 

 give the blue colour with guaiacum tincture alone. Those, of which the 

 extracts only bring about blueing on addition of hydrogen peroxide, are 

 said to contain a peroxidase (Chodat, 1). 



Expt. 112. Demonstration of the presence of an oxidase. Take a portion of a fresh 

 Potato tuber and pound well in a mortar with a little water. Filter, and to the 

 extract, in a white evaporating dish, add a few drops of 1 % guaiacum solution in 

 alcohol. The guaiacum tincture will be found to give a blue colour at once with the 

 potato extract. 



A control tube should be prepared by well boiling some of the water extract of 

 the tuber, cooling and then adding guaiacum. No colour is produced, owing to the " 

 fact that the enzyme has been destroyed by boiling. Other tissues which may be 

 used to demonstrate the above reactions are : root of beet and fruits of apple, pear 

 and plum. 



Guaiacum gum is obtained from two West Indian species of Guaiacum trees, 

 G. officinale and G. sanctum, partly as a natural exudation and partly by means of 

 incisions. It gives a yellow solution with alcohol which contains guaiaconic acid, 

 and the latter, on oxidation, yields guaiacum blue. As far as possible, inner portions 

 of the resin lumps should be used, as the resin oxidizes in air, and then may give 

 unreliable results. It is best to make the tincture freshly before use, and, as a 

 precaution, to boil it on a water-bath with a little animal charcoal and filter. 

 Guaiacum gum tends to form peroxides on exposure to air, and these are removed by 

 the above treatment. 



