PHYSIOLOGICAL OXIDATIONS. 971 



Or, as seems probable from some recent experiments,* the peroxidase 

 may first combine with the oxygen of the oxygenase to form a per- 

 oxide, which then reacts with the oxydizable material in the tissues. 



P + AO, = PO2 + A 

 B + PO2 = PO + BOorP + 2B0 



This view simplifies the somewhat confusing distinction made in 

 the literature between oxidases, or enzymes which act in the pres- 

 ence of oxygen, and peroxidases which act only in the presence of 

 peroxides, since it is assumed that oxidases, properly speaking, do 

 not exist. What has been designated as an oxidase or a direct 

 oxidase is simply a mixture of a peroxidase and an oxygenase. It 

 has been found that man}^ of the characteristic oxidations that 

 occur in the body, such as the oxidation of the fatty acids at the 

 /3-carbon atom in the chain, the oxidation of glucose to glycuronic 

 acid, etc., may be imitated outside the bod}^ by oxidation with 

 hydrogen peroxide, but not by other oxidizing agents, f This 

 collateral evidence gives important support to the theory. Per- 

 oxidases have been discovered in the blood, milk, and in several 

 of the tissues of the body, such as the lymphocytes, sperm cells, 

 etc.f They can be tested for by a number of reactions, chiefly 

 color reactions, such as the bluing of a tincture of guaiacum in the 

 presence of a peroxide or the conversion of a colorless or leucobase to 

 a colored oxidation product. Some of these peroxidases have been 

 given specific names in accordance with the particular compounds 

 whose oxidation they effect. For example, xanthinoxidase , which 

 effects the oxidation of hypoxanthin and xanthin to uric acid; the 

 glycolytic oxidase or oxidases, which effect the oxidation of the 

 intermediary products of sugar metabolism in the tissues; tyrosin- 

 ase, which effects the oxidation of ty rosin, and in this way is sup- 

 posed by many observers to give rise to various animal oigments, 

 such as melanin; the aldehydases, which effect the oxidation of alde- 

 hydes to their corresponding acids — salicyhc aldehyd, for instance, 

 to salicylic acids. In practically all of the tissues there exists an 

 enzyme which is capable of breaking up hydrogen peroxide with 

 the liberation of oxygen. The evolution of oxygen is readily seen 

 when a solution of hydrogen peroxide is brought into contact with 

 a living tissue. This peroxidase has been given a special name, 

 catalase, but its relations to the processes of phj^siological oxidation 

 have been interpreted in different ways by the various workers in 

 this field. Burge § has brought forward considerable experimental 



* Reed, "Botanical Gazette," vol. 62, 1916. 



t Consult Dakin, "Oxidations and Reductions in the Animal Body," 1912. 

 t For discussion and literature consult Kastle, "The Oxidases," Bulletin 

 No. 59, 1910, Hygienic Laboratory, Washington, D. C. ; also Bach, loc. cit. 

 § Burge, "American Journal of Physiology," vols. 41-43, 1916, 1917. 



