26 



juice of the lac tree and converts it by oxidation into a black substance. 

 Laccase is killed at 75.5o C. (I680 F.) and gives tlie gnaiac reaction 

 without the aid of hydrogen peroxide. Like laccase, the oxidases of 

 Seyiecio vulgaris^ Lactuca sativa, and Taraxacum dens leonis fail to attack 

 tyrosin. In certain objects, especially in fungi, however, laccase and 

 tyrosinase occur simultaneously. 



The oxidation of polyvalent phenols by laccase leads not only to 

 organic acids, but even to the production of carbonic acid. Bertrand 

 observed in one case that for 23.3 cc. absorbed oxygen as much as 13.7 

 cc. of carbonic acid were produced. 



Gouirand has observed in certain spoiled wines an oxidase^ which 

 oxidizes the coloring matter, the tannin, and the alcohol of the wine, 

 with production of carbonic acid. This oxidase is destroyed in plain 

 aqueous solution at 72.5o C. (162.5o F.), while in the wine a temperature 

 of 60° C. (1400 F.) suffices. Very small doses of sulphurous acid will 

 also kill it. It is supposed to be derived from the fungus BotryUs 

 cinerea^ which frequently grows upon ripening grapes,^ while Martinand 

 and Tolomei observed an oxidase in ripe grapes. As to the Florida 

 tobacco leaf, the writer has demonstrated the presence of a relatively 

 large amount of oxidases in it. 



These oxidizing enzyms belong, like other enzyms, to the i^rotein 

 compounds, forming a special group of labile proteins, i. e., proteins 

 containing much chemical energy, which on the one hand is the cause 

 of tbeir activity and on the other of their changeability to indifferent 

 proteids by heat, acids, and i^oisons. They are, as it is expressed, 

 easily killed. The labile, active atomic groups in the molecules change 

 thereby, the atoms migrating into more stable position. 



Yieios on the physiological functions of the oxidizing enzyms. — As to 

 the physiological function of the oxidizing enzyms, no perfectly satis- 

 factory explanation has thus far been j^roposed. Some authors sup- 

 pose that they are important agencies in the respiration process and 

 that even respiration itself is caused by them when they are supported 

 by certain properties of the living protoplasm. This is, however, 

 improbable for several reasons: (1) Not every plant contains oxidizing 

 enzyms j (2) many plants contain them only in certain stages; and (3) 

 carbohydrates and fat, the materials which by their combustion serve 

 for support of the respiration and for the production of energy, are not 

 attacked by the oxidizing enzyms, bat are attacked very energetically 

 by the protoplasm. 



Portier believes that the oxidase of the blood, of which he made a 

 special study, serves to augment the vitality of the leucocytes, which 

 prepare the oxidase and finally deliver it up to the blood when they 

 die. This hypothesis will certainly not find support. The suggestion 

 has also been advanced that the oxidizing enzyms play in plants the 



iThis anoxidase is supposed by Bertrand to be identical with laccase. 

 2 See also Cazeneuve, Corapt. rend., Vol. CXXIV. 



