588 



various observers and ascribed to "reductases" or " reducases." In analogy with 

 the oxidase system, as 



peroxidase + peroxide 

 we may regard a reducase as 



Schardinger's enzyme + aldehyde. 



Schardinger's reaction appears then to be a hydrolytic-oxidative-reduction process, 

 in which the aldehyde is oxidised by the oxygen of water, while the hydrogen thus 

 set free reduces the methylene blue to its leuco-base, by the intermediation of the 

 enzyme. 



Liver tissue, ground up with water, has been known for a long time to be capable 

 of reducing methylene blue at a rapid rate. Bach (1911-1912) investigated this 

 reaction from the above point of view. Is there an enzyme present like that in 

 milk and an oxidisable substance acting like aldehyde ? 



If liver is rubbed up with five times its weight of 2 per cent, sodium 

 fluoride and filtered through linen, the emulsion, diluted five times, has very little 

 action by itself on methylene blue. But, if a small quantity of acetic aldehyde be 

 added, the reduction is rapid. If previously boiled, the emulsion has lost this 

 property. Filtration through paper deprives it of the enzyme, which remains 

 on the paper. But a solution can be made by extracting the liver with 1 per cent, 

 sodium bicarbonate. This is filtered through linen, the filtrate neutralised exactly 

 with acetic acid and again filtered through paper. Alcohol produces a precipitate 

 in the filtrate, and, from this precipitate, the enzyme can be extracted by half per 

 cent, sodium bicarbonate. The solution reduces methylene blue in the presence of 

 aldehyde. The enzyme is very unstable. A similar preparation can be made 

 from lung, spleen, kidney, or thymus. 



This enzyme also reduces nitrates to nitrites in the presence of an aldehyde, 

 just as fresh milk does, so that it is not of a specific nature. 



The nature of the substance which takes the place of aldehyde in the cell 

 system is not yet known. It appears to be insoluble, since it is left with the cell 

 debris on the linen in Bach's process, as given above. 



An oxidase (or phenolase) produces its oxidation by the aid of free oxygen, 

 while the reducase acts by means of the combined oxygen in water, indirectly. 

 Thus: 



oxidase = peroxidase + oxidisable substance (oxygenase) + oxygen 



reducase = Schardinger's enzyme + oxidisable substance (oxygenase) + water. 



In the first case, we may say that free oxygen is reduced, but the reduction 

 process stops here and is covered by the oxidation process ; in the second case, 

 hydrogen is set free by the decomposition of the oxidising agent, water, and further 

 reduction processes are set in progress. 



Cannizzaro's Reaction. This reaction consists in the simultaneous oxidation 

 and reduction of aldehydes, by which the hydrogen of water converts one molecule 

 to the alcohol and the oxygen converts the other one to the acid : 



2R.CHO + 2HOH = R.CH 2 OH + R.COOH + H 2 O. 



Parnas (1910, 2) showed that liver tissue greatly accelerates this reaction, a result 

 which is obviously an aspect of the action of Bach's perhydridase. 



The enzyme in extracts of organs which oxidise salicylic aldehyde appears to 

 be similar and the reaction to be a case of acceleration o'f Cannizzaro's reaction. 



Plant Reducases. There is a perhydridase in potato juice and other plant 

 extracts (Bach, 1913, 2). This requires for its action the presence of one of the 

 lower aldehydes and then reduces nitrates to nitrites, but apparently methylene 

 blue is not attacked. 



The increased consumption of oxygen by acetone yeast in the presence of 

 methylene blue, as described by Meyerhof (1912, 3), seems to be a related 

 phenomenon. The experiments of Palladin, Hubbenet, and Korsakov (1911) on 

 the higher plants also bear upon the question. Methylene blue causes greater 

 oxidation in etiolated plants and the presence of oxygen is necessary for the effect 

 in the bean plant, although not in the pea ; a fact which appears to be connected 



