298 Prof. A. J. Ewart. Comparative Study of Oxidation by 



on which previous!}' it had little or no action. The readiness with which 

 apple pulp or its extracted oxidase oxidises ursol tartrate and tannic acid is 

 therefore apparently due to the presence of a phosphatic sensitiser. Potato 

 pulp contains phosphates in less amount and in less readily soluble form but 

 if a living slice of potato is immersed in boiled apple sap, a brown layer of 

 oxidised tannic acid slowly forms on the surface where the oxygen and tannic 

 acid come into contact with oxidase and traces of phosphates under optimal 

 conditions for progressive oxidase action. In the living cell the permeability 

 of the cell membrane may determine whether an oxidase and its sensitiser 

 come into contact simultaneously, singly or not at all with an oxidant 

 substance. 



The Relation behveen the Action of Metallic Oxidases and that of an Enzyme. 



This question has been fully investigated by H. E. and F. Armstrong, in a 

 long series of papers by themselves and pupils, so far as acids and hydrolysing 

 enzymes are concerned. A few data in regard to certain inorganic oxidases 

 are given beneath, and firstly in regard to the dilution at which a perceptible 

 action is shown. Ferric chloride will give a perceptible blue with guaiacum 

 down to a concentration of O'OOOl per cent., while copper sulphate in the 

 presence of salt gives a faint blue clown to O'OOOOl per cent. With a 1-per- 

 cent, solution of ursol tartrate in the presence of an equal volume of 1-per-cent. 

 hydrogen peroxide a distinct acceleration of oxidation is shown down to a 

 concentration of O'OOOl per cent, of ferric chloride (0-00003 per cent, in total 

 solution). The oxidation of hydroquinone in the presence of hydrogen peroxide 

 is accelerated by the addition of an equal volume of 0'001-per-cent. ferric 

 chloride but not perceptibly so by lesser dilutions. 



One property of an oxidase enzyme is that it may transfer oxygen from 

 one labile compound to another. In the following experiment equal volumes 

 of 1-per-cent. hydroquinone and of ferricyanide of potassium and hydrogen 

 peroxide were mixed, and the time taken to reach a standard shade of brown 

 noted. The top line of the Table gives the concentration of the substance 

 whose amount was varied. The lower rows give the time in minutes required 

 to cany the oxidation to the same stage in each case, and the figures in brackets 

 are the products of the time of reaction multiplied by the concentration of 

 the variant substance. In experiment A, to each 5 c.c. of 1-per-cent. 

 hydroquinone, and of 1-per-cent. hydrogen peroxide, 5 c.c. of potassium 

 ferricyanide of varying concentration were added. In experiment B the 

 hydrogen peroxide was in diminishing concentration ; and in C, both the 

 hydrogen peroxide and potassium ferricyanide decreased in concentration 

 correspondingly. 



