i 9 2o] ROSE, KRAYBILL, &■ ROSE— OXIDASE ACTIVITY 220 



Wolff found tyrosinase from Russula delica most active in a 

 solution neutral to phenolphthalein, and Abderhalden and Gug- 

 genheim (1) found that tyrosinase is destroyed by 0.016 N hydro- 

 chloric acid, and greatly retarded by 0.016 N sodium hydroxide. 

 Rose (28) showed that the decrease in oxidase activity, as observed 

 in the Bunzell apparatus, is due to an increase in the hydrogen ion 

 concentration of the medium. Reed (27) found oxidase activity 

 in potatoes and apples inhibited even by low hydrogen ion con- 

 centrations; and likewise Bunzell (9) found the action of oxidase 

 retarded with increasing hydrogen ion concentrations. 



Methods 



All but one of the experiments described in this paper were made 

 with portions of apple bark which had been dried at 35-40° C. 

 for 2-3 hours, ground line enough to pass through a 40-mesh wire 

 sieve, and stored air dry in zinc-capped Mason jars. One experi- 

 ment was made with solutions of precipitated oxidase separated 

 from aqueous extracts of healthy bark and of diseased bark by the 

 addition of about 10 volumes of alcohol. In order to obtain the 

 precipitated oxidase, 2 gm. of bark were allowed to stand in a 

 beaker with 10 cc. of water and 5 drops of toluol for 1 hour. The 

 extract was then squeezed out through moist cheesecloth on coarse 

 filter paper. The beaker was washed with five 1 cc. portions of 

 water and the filter paper finally with two more. There was then 

 added 50 cc. of 95 per cent alcohol to the filtrate (concentration of 

 alcohol about 70 per cent) and the whole allowed to stand for 

 10 minutes. The flocculent precipitate which had formed was 

 collected on a hard filter by gentle suction with a filter pump. 

 There was then added 150 cc. more alcohol to the filtrate (con- 

 centration of alcohol now about 90 per cent) and the whole 

 allowed to stand for 1 hour, since precipitation was slow, before 

 this second fraction was collected on the filter with the first. 

 The precipitate was dissolved in water and used immediately, as 

 described later. 



The stock solutions of all of the salts tested were made to a 

 concentration of 0.5 N. Potassium chloride, manganese chloride, 

 ferrous chloride, and ferric chloride were used also in the additional 



