OXIDIZING ENZYMES 413 



example which is very familiar to biological chemists is that afforded 

 by the action of alkaline copper salts upon glucose. If a limited 

 quantity of Fehling's Solution be run into a boiling solution of glucose 

 the solution is decolorized and, the red cuprous oxide is precipitated, 

 but upon exposing the mixture in a shallow vessel to the air, the 

 cuprous oxide again takes up oxygen, passes into solution and tinges 

 the fluid blue. If the mixture be now boiled, the cupric hydroxide 

 again parts with its oxygen to the excess of glucose, so that if the process 

 be repeated a sufficient number of times a limited quantity of Fehling's 

 solution will oxidize a relatively unlimited quantity of glucose. This 

 is, in fact, the chief pitfall in the practical employment of Fehling's 

 method of sugar estimation. In a similar manner many other metal 

 oxides are capable of acting as activators or carriers of oxygen. 



According to Bach and Chodat the oxidizing enzymes which occur 

 in the majority of living tissues in reality consist of two parts: the 

 one part, the Oxygenase, playing the role that cuprous oxide plays in 

 the oxidation of sugar, namely that of a carrier of oxygen, while the 

 other part, the Peroxidase, facilitates the transfer of the oxygen from 

 the oxygenase to the material which is undergoing oxidation. Hydrogen 

 Peroxide may in many cases take the place of the oxygenase, and hence 

 we obtain the blueing of guaiacum tincture when blood or a tissue- 

 extract together with hydrogen peroxide act upon it. The function of 

 the manganous salt in Laccase appears to be associated with the 

 oxygenase fraction, while in many oxidizing ferments found in animal 

 and other plant tissues, Iron plays the role which manganese plays in 

 determining the activity of laccase. In this connection it is of great 

 interest to note that Hemoglobin is itself an oxygenase, and that, 

 according to Bertrand, the Benzidine and Guaiacum tests for blood are, 

 in actuality, tests for hemoglobin. 



The majority of the oxidizing enzymes appear to be substances of a 

 complex character, in many cases either protein in nature or closely 

 associated with protein. It is probable that the majority of the 

 oxygenases or oxygen-carriers are bodies analogous in complexity to 

 hemoglobin and, like hemoglobin, containing iron or some other polyv- 

 alent metal as an integral portion of the molecule. On the other hand 

 Euler and Bolin have shown that the Laccase from Medicago saliva 

 is a relatively simple substance, being a mixture of the calcium salts of 

 aliphatic hydroxy-acids. A synthetic mixture of the calcium salts of 

 glycollic, citric, malic and mesoxalic acids was found by them to exert 

 the same action in accelerating the oxidation of polyphenols as the 

 natural laccase. This enzyme is, of course, thermostabile. 



An important group of oxidizing enzymes is that of the Tyrosinases 

 which convert tyrosine into dark-colored substances of complex struc- 

 ture known as Melanins, which are probably identical with or closely 

 allied to many naturally-occurring pigments. These enzymes are 

 found in many vegetable tissues and von Furth has also found them 

 in the tissue-fluids of many insects and in the ink-sac of the cephalopod 



