30 



may be caused by an another enzyme and then it is upon this 

 intermediate product that tyrosinase acts, finally giving the 

 black melanin. The earlier workers considered that tyrosinase 

 was a specific enzyme acting only on ty rosin, but in the course 

 of time it has become evident that tyrosinase is specific in the 

 same sense as laccase; namely, it acts upon a group of compounds 

 closely related in structure. 



Just as it is possible to obtain anti-toxins, research has shown 

 that we may obtain anti-enzymes. In this place we are con- 

 cerned only with the anti-oxidases, which have been produced 

 in the usual manner, that is, by the repeated injection of small 

 though increasing amounts of the enzyme preparation into a 

 rabbit or other animal, and the withdrawal of some of the blood 

 after immunity has been established to that particular enzyme. 

 The blood serum from such immune animals prevents or retards 

 the natural oxidizing action of the enzyme under investigation. 

 Gessard^^ obtained anti-tyrosinase and anti-laccase that com- 

 pletely inhibited the oxidizing power of the corresponding plant 

 enzyme preparations. We shall see later that anti-oxidases may 

 play an important part in the physiology of the plant. 



Generally speaking, tyrosinase seems to be the nearest to the 

 true enzyme of any of the oxidases with which we are acquainted. 

 It is most specific in its action, most sensitive to exterior con- 

 ditions, and up to the present, has not been replaced by any 

 artificial enzyme in the oxidation of tyrosin to a melanin. It 

 is usually associated with laccase in plants, but the presence of 

 laccase does not indicate the appearance of tyrosinase, while on 

 the other hand, the latter is almost invariably accompanied by 

 laccase. 



As in the case of laccase, Bach^^ claims that the tyrosinase is 

 really composed of two parts, oxygenase and the peroxidase. 

 He found that by the use of alcohol precipitations he was able 

 to reduce the activity of the tyrosinase of the potato, as previ- 



i^Gessard. (a) Anti-laccase. Compt. Rend. Soc. Biol. 139: 644. 1904. {b) 

 Sur la tyrosinase. Ann. Inst. Pasteur 15: 593. 1901. 



IS Bach. Ueber die Wirkungsweise der Tyrosinase. Ber. Chem. Gesell. 41 : 221. 



