OXIDASES OR OXIDISING ENZYMES. 257 



With a boiled solution of laccase no such change can be 

 observed. 



So far as Bertrand has investigated the properties of 

 laccol, it appears to be allied to certain polyatomic phenols. 

 On this account he has examined the action of laccase on 

 several of the latter, especially hydroquinone and pyro- 

 gallol (3). When the former is submitted to its influence 

 the colour of the solution quickly becomes rose-red, and 

 after a short interval crystalline scales with a green metallic 

 lustre appear, the quantity rapidly increasing. When this 

 operation is carried out in a sealed tube the oxygen present 

 is absorbed almost completely. The liquid gives off a 

 strong characteristic odour, and after the solid matter is 

 separated, quinone can be extracted from it by shaking 

 with ether. The precipitate is quinhydrone. 



In the absence of the laccase, or if that employed is 

 previously boiled for a few minutes, the hydroquinone does 

 not absorb oxygen, nor undergo alteration. The hydro- 

 quinone is therefore oxidised by the free oxygen under the 

 influence of the laccase. 



2 C 6 H 4 (O H) 2 + O a = 2 H 2 O + 2 C 6 H 4 2 



The colour given to the liquid is due to the formation 

 of the quinone, and some of it, combining with the excess of 

 hydroquinone not oxidised, produces the less soluble crystals 

 of quinhydrone. When pyrogallol is used instead of hy- 

 droquinone, similar results are obtained, a precipitate of 

 purpurogalline being thrown down in the form of a powder, 

 which on heating sublimes, forming orange-red needles 

 which are soluble in alcohol and acetic acid. 



Laccase attacks many other polyphenols but only those 

 whose phenolic oxhydriles are in the ortho- and para- 

 positions in the benzine ring (4). Those with metaposition 

 are affected only with difficulty. The oxidisability of these 

 bodies by laccase seems to depend on the facility with 

 which they can be transformed into quinones. The mono- 

 phenols are not oxidised by the enzyme, but it attacks 

 gallic acid and tannin. 



Bertrand's observations on the behaviour of laccase 

 at different temperatures do not agree with those of 



