446 



A. G. PASYNSKIÏ 



of the enzyme preparation (dissolved in i ml of water) was added to 25 ml of 

 a mixture of equal volumes of i-2% ascorbic acid and 0-2% hydrogen peroxide. 

 During the course of the reaction samples of 01 ml of the solution were removed 

 every 10 min and their ascorbic acid content was determined by titration with 

 o-ooi M-KIO3 in the presence of KI, the completion of the reaction being in- 

 dicated by the starch -iodine reaction. The titrations were reproducible to within 

 0-02 ml, i.e. o-2-o-3% of the amount being measured. The removal of the 

 samples did not disturb the progress of the reaction as they constituted only 

 0-4% of the volume of the solution, which did not have any significant effect 

 on the course of the curve. 



When the experiment was carried out under static conditions (in a glass at 

 20° C, pH 3-0) the ascorbic acid content in a mixture of equal volumes of 1*5% 

 ascorbic acid and o-iP/,., hydrogen peroxide fell according to a uniform curve 

 for many hours (Fig. i) which was somewhat steeper when the enzyme was 

 added. 



"0 1 2 3 4 5 



Fig. I. Kinetics of oxidation of ascorbic acid under static conditions. 



The curve corresponds closely with that for the equation for a reaction of the 

 second order with a velocity constant K = 2-2 x io~^ 1/mole-sec. Owing to 

 the irreversibility of the reaction A-*D the equihbrimn state was not reached in 

 the experiment. 



The experiments under stationary conditions were carried out in the apparatus 

 shown in Fig. 2. The reacting mixture was placed in the cylinder A with a 

 cellophan membrane stretched over the bottom. Three sizes of apparatus were 

 used, the diameters of the membranes being I, i-6; II, 2-4; III, 37 cm. 

 Cylinder A was placed in vessel B through which there was a constant flow of 

 thermostatically controlled distilled water (in most cases at 20^ C), bathing the 

 outside of membrane C and flowing out over the edge of the vessel into a receiver. 

 Both the reacting solutions were continuously admitted to cylinder A from 

 vessels D and D' through narrow capillary tubes (r = o-i mm) the ends of which 

 were submerged in the solution. The concentration of hydrogen peroxide in the 

 solution being admitted was the same as that in the original solution, while 

 that of ascorbic acid was somewhat higher (in cylinders I and II S = 1-5% or 

 0-0852 M, in cylinder III 5 -^ 2-5% or 0-142 m). The flow of the reacting 



