240 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



to the quantity of peroxidase and of peroxide. It is, how- 

 ever, independent of the quantity of substrate, provided 

 the latter is present in sufficient excess. The actual weight 

 of substrate must be far greater than the maximum amount 

 that could be oxidized in the time. It seems probable that 

 what is needed is sufficient pyrogallol to keep the surface of 

 the peroxidase saturated with it by adsorption. 



METHODS FOR ESTIMATING TYROSINASE. 



Von Ftirth and Jerusalem (1907) investigated the action 

 of tyrosinase by determining the quantity of melanin 

 resulting from its action on tyrosin. This they effected by 

 a spectro -photometric method, and by the hsematokrit. 

 The sedimentation of the pigment was brought about by 

 boiling with calcium chloride, and the volume of the deposit 

 measured in a graduated centrifuge tube. Bach (1908), 

 however, found that the brown pigment produced by the 

 action of the enzyme upon tyrosin can be oxidized further 

 to a colourless compound by a dilute acid solution of per- 

 manganate. This process can be rendered quantitative 

 by the use of 0-002 N permanganate, and is both the 

 simplest and the most accurate method for the measure- 

 ment of tyrosinase activity. 



MANOMETRIC METHODS OF MEASURING OXIDASE 

 ACTIVITY. 



However, the most fundamental quantity to measure 

 seems to be the amount of oxygen absorbed. This also 

 permits of investigations being made upon the action of 

 an enzyme on various substrates and under diverse con- 

 ditions in a strictly comparable manner. 



The method was adopted by Foa (1908), and by Mathews 

 (1909) in his work on the oxidation of the sugars. More 



