60 SCIENCE PROGRESS 



therefore, very interesting to determine whether the carbon- 

 monoxide-haemoglobin, a pigment with a well-known spectrum, 

 would remain unaltered in the presence of reductase, or whether 

 it would be in any way changed. It remained unaltered for 

 many hours at 40 C, showing that reductase in its state of 

 comparative freedom in tissue juice was as powerless to break up 

 the carbon-monoxide-haemoglobin union as it is in intact cells. 



Recently we have studied the enzymic nature of the active 

 agent of tissue juice from the kinetic standpoint. Measure- 

 ments were made to determine the value of the temperature 

 coefficient of the activity of reductase, and also to determine 

 the nature of the law governing the decay in the activity of 

 the enzyme. As regards the former, we obtained the necessary 

 data from experiments on the reduction of oxyhaemoglobin by 

 cat's liver juice at different temperatures. To determine the 

 temperature coefficient, the time required to reduce oxyhaemo- 

 globin at any one temperature was divided by the time required 

 to reduce it at a temperature io° higher. Between 10 and 40° C. 

 the velocity of reduction is approximately doubled for each io° 

 rise in temperature, so that the temperature coefficient is 

 about 2. This discovery as to the behaviour of tissue juice with 

 rise of temperature confirms our general contention that we are 

 dealing with an enzyme. Above 40° it has been found that the 

 increase in the velocity of reduction with rise in temperature 

 rapidly falls off. Between 50 and 6o° C. the temperature co- 

 efficient has been found to be 1*43. Although usually the 

 temperature coefficients of reactions decrease slightly with 

 increase of temperature, the decrease in the values obtained for 

 the reduction of oxyhaemoglobin by reductase at temperatures 

 above 40 C. is much greater than would be the case in ordinary 

 chemical reactions. Since it is exceedingly probable that the 

 optimum temperature of reductase lies between 40 and 46" C, 

 the acceleration of the velocity of reduction due to increase in 

 temperature is evidently to a certain extent counteracted by 

 a partial inhibition or destruction of the enzyme, the result 

 being a decrease in the value of the temperature coefficient. 



Mathematical treatment of our data shows that if the decrease 

 in activity of the enzyme be regarded as proportional to the 

 decrease in its reducing power, then the expression 



«?lkr l0 S'»(dbH 



