498 ENZYMES 



Neuberg * even goes so far as to suggest that the phosphate 

 relations of yeast juice, represent an artificial condition, and 

 states that bottom fermentation yeast will only synthesize 

 hexosephosphate when treated with a protoplasmic poison 

 such as toluene. 



OXIDASES. 



The oxidases are enzymes which have the power of oxi- 

 dizing various aromatic compounds and chromogens, which 

 action is, in the latter case, indicated by a change in colour. 

 The change in colour in vegetable tissues on exposure to air 

 is an everyday phenomenon ; the exposed surfaces of an apple, 

 especially cider varieties, will rapidly turn brown. The 

 darkening in the colour of raw rubber is also due to an 

 oxidase which is associated with the protein of the coagulated 

 latex.f 



These changes are often of considerable economic impor- 

 tance ; thus the discoloration of sap wood markedly depreciates 

 the value of timbers, $ while the lacquer industry of China 

 and Japan has been built up on the facts relating to the action 

 of the oxidase, laccase, on the expressed sap of species of 

 Rhus (see below). 



Oxidases are very widely distributed in the vegetable 

 kingdom ; in the higher plants they may occur in any organ 

 — stem, root, leaf, laticiferous tissue, petals, and fruits. 



According to Wheldale-Onslow,§ oxidases are present in 

 about 63 per cent of the higher plants. As a rule all the genera 

 of an order contain oxidases or peroxidases ; thus oxidase 

 orders are Gramineae, Labiatse, Umbelliferae, Boraginaceae, 

 Solanaceae, and Compositse, while peroxidase orders are 

 Liliaceae, Cruciferae, and Crassulaceae ; orders containing both 

 oxidases and peroxidase plants are Ranunculaceae, Rosaceae, 

 and Leguminosae. 



A distinction is made between oxidases and peroxidases in 



♦Neuberg: '•Biochem Zeit.," 1920, 103, 320. Neuberg, Farber, 

 Levite and Schwenk : id., 1917, 83, 244. 



t Spence : " Biochem. Journ.," 1908, 3, 165, 351. 



X Bailey : " Bot. Gaz.," 1910, 50, 142. 



§ Wheldale-Onslow : " Biochem. Journ.," 1921, 15, 107. 



