SOME RECENT WORK ON PLANT OXIDASES 115 



or pyrogallol, were said to contain an oxidase, whilst those 

 which required the addition of a peroxide such as hydrogen 

 peroxide or a spontaneously oxidised essential oil were described 

 as containing a peroxidase. The view that an oxidase consisted 

 of a peroxidase and a naturally occurring peroxide was put 

 forward by Kastle and Lcevenhart, 1 and has gained very general 

 acceptance. Keeble and Armstrong 2 record that in certain 

 flowers the organic peroxide accumulates during darkness, so 

 that apparently the tissues contain oxidase at one time and per- 

 oxidase at another. The author's own 3 observations on foliage 

 leaves also point to the variability of the quantity of the peroxide 

 in any tissue. At present it is usual to refer to the " direct " 

 oxidase action, or to the "indirect" action, when the addition 

 of a peroxide is required to bring about oxidation. Strictly 

 speaking it would be more correct to refer to both as peroxidase 

 actions, for the essential is that a peroxide is split up and 

 oxygen derived from it is transferred to an easily oxidisable 

 substance. That hydrogen peroxide does not occur in any 

 appreciable quantity in the tissues is proved by the almost 

 universal presence of catalase, an enzyme which decomposes 

 this substance, but does not attack the closely related ethyl 

 hydroperoxide or any other peroxide, so far as is known. 



How far the oxidases are specific in their action seems to 

 be in doubt. Five different oxidases at least have been described 

 as occurring, or rather five different classes of oxidases, viz. lac- 

 cases, tyrosinases, alcoholases, purine oxidases, and aldehydases. 

 The laccases or phenolases which act on many phenols and are 

 very widely distributed in plants, and the tyrosinases which 

 act on tyrosin or polypeptides containing tyrosin to produce 

 a body which further reacts with amino-acids yielding dark- 

 coloured pigments termed melanins, as shown by Abderhalden 

 and Guggenheim. 4 An example of the alcoholases is furnished 

 by the enzyme which converts ethyl alcohol into acetic acid and 

 is found in certain bacteria. The purine oxidases have been 

 extracted so far from animal tissues only, and the existence of 

 the aldehydases is still hypothetical. 



1 Kastle and Lcevenhart, Amer. Chem.Journ. 1901, 26, 539. 



3 Keeble and Armstrong, Journ. Genetics, 1912, 2, No. 3, 277. 



5 Atkins, W. R. G., Set. Proc. R. Dubl. Soc. 191 3, U(N.S.), 144. 



4 Abderhalden and Guggenheim, Hoppe-Seylers Zeitschr. f. physiol. Chem. 

 1908, 54, 331. 



