OXIDATION AND REDUCTION 585 



formed when air is admitted by taking up of oxygen in the process of autoxidation 

 of a spontaneously oxidising substance. 



This system of autoxidisable substance, peroxide and peroxidase, is that which 

 was at one time thought to be itself an enzyme and called an "r^drtftf" The 

 actual enzyme concerned is peroxidase, as was shown by Bach ancTChodat (1904) ; 

 the other constituent, which forms a peroxide in presence of oxygen, is called by 

 them, " oxygenaseJi- Oxidase is, in fact, separated into two constituents, each 

 inactive until mixed. 



It may be noticed that the termination "ase" implies enzyme nature, but we have seen 

 reason for regarding the production of peroxides in autoxidation as not being of the nature 

 of catalysis. It does not seem to me, moreover, that the easier destruction by heat of the 

 oxygenase than the peroxidase proves its enzyme nature. In this respect, I am in agreement 

 with Moore and Whitley (1909), but it is, after all, only a question of the meaning of the word 

 "catalyst." Otherwise the scheme of Bach satisfies the facts excellently. 



We may summarise the matter thus : the substrate, which is to be subjected to 

 oxidation, is usually one that, by itself, takes up oxygen by autoxidation so slowly 

 as to be imperceptible. This is accelerated by the presence of a genuine autoxidis- 

 able substance (Bach's " oxjgenase "), which acts in a way similar to that of oil 

 of turpentine and such readily oxidised substances. This action is produced by 

 the formation of peroxides. These peroxides are rendered still more active by 

 the enzyme, peroxidase. which accelerates the transfer of oxygen to the substrate 

 by splitting it off from the peroxide. The value of the enzymic last part of the 

 process may be this. We saw that the oxidation of an autoxidisable substance 

 may effect the oxidation of other substances present during the reaction itself, so 

 that it necessitates the presence of both free oxygen and an easily oxidised sub- 

 stance. The peroxide formed in this reaction, on the other hand, may very well 

 persist for an appreciable time and be thus available for the bringing about of 

 an oxidation when acted on by peroxidase coming into play as required. 



We have seen above that salts of iron, manganese, or copper act on peroxides 

 in the same way as the enzyme, peroxidase, and Bertrand thought that his " laccase " 

 owed its activity to the presence of manganese. It was found later that iron__ 

 could take the place of manganese, and Bach (1910) states that he "has 

 prepared " oxidases " free frombolh these metals; whether any other metal, 

 acting similarly, was present is not stated. The hypothesis that peroxidases are 

 particularly active forms of one of these metals is, at present, the one most in 

 agreement with experimental facts. 



The metals found to be active as "peroxidases" are those capable of existing in 

 two states of different valency. 



By the addition of one of these metallic salts to a system of peroxide and 

 peroxidase, a mixed system can be produced, with increase of activity. 



Further, Dony-Henault (1908) has prepared what he calls an "artificial . 

 laccase " in the following way. A solution is taken containing, in 50 c.c. of water, 

 1 g. manganese formate, 0'4 g. sodium bicarbonate, and 10 g. gum arabic. This is 

 precipitated by alcohol. The precipitate is redissolved in water and again thrown 

 down by alcohol. This substance is of interest for two reasons: 1. As an 

 obvious adsorption compound, but yet precipitated unchanged by alcohol, no 

 doubt because the precipitation is practically total. 2. As an enzyme made 

 artificially. It is precipitated by alcohol. But the more important property is 

 that it acts catalytically. It does not seem to be destroyed by heat, but a similar 

 substance made from albumin and manganese by Trillat (1904) is destroyed by 

 boiling, while it has been stated that natural laccase is not so destroyed. The 

 property clearly depends on the nature of the emulsoid colloid in association with 

 the metal. 



The natural " oxidase-^-systems are more or less " specific " : each appears to act 

 on a special group of substrates, or even on one only. There is reason to suppose 

 that this depends on the particular organic peroxide constituent of the complex 

 system, rather than 011 the peroxidase. This " specificity " is not unknown in 

 inorganic catalysts, thus Wolff (1908) found that colloidal ferrous ferrocyanide acts 

 as a peroxidase towards phenols, but does not accelerate the action of hydrogen 



