VELOCITY OF REACTION 65 



still, very different expressions were obtained for the law of 

 velocity of reaction of the same enzyme upon the same sub- 

 stratum, and it is only recently by the observations of Henri, 

 Horace Brown and Glendinning, E. Frankland Armstrong, and 

 Bayliss that we are beginning to be able to understand the 

 results, and to bring the different observations into accord with 

 one another. 



O'Sullivan and Tompson were the first observers who studied 

 the velocity of action of an enzyme quantitatively throughout 

 the course of the reaction. 1 They employed the action of invertase 

 on cane-sugar, and found that the reaction was mono-molecular, 

 obeying the mass action law, and giving a logarithmic curve. 

 Henri, however, who later worked at the same subject, found 

 that the value of the constant K, derived from their figures, by 



using the formula deduced above (p. 58), K = - log - , did not 



t Q> X 



remain quite constant throughout the reaction, but slowly in- 

 creased in value in the ratio, for example, of 298 near the begin- 

 ning to 332 near the close of the reaction, thus showing that 

 the velocity of reaction only approximated to the logarithmic 

 law. 



Tammann, in a series of researches, investigated not only the 

 action of invertase on cane-sugar, but of emulsin on different 

 glucosides (salicin, amygdalin, arbutin, sesculin), and found that 

 the reaction never proceeded to completion. He observed that 

 the velocity of reaction was retarded in increasing amount by 

 the presence of the products of reaction as these accumulated in 

 solution. The percentage which remained unconverted varied 

 with the temperature, the concentration of ferment, and 

 the concentration of substratum. Increasing . the temperature 

 caused the reaction after it had come to rest at the lower 

 temperature to recommence and proceed further towards com- 

 pletion. With a constant quantity of enzyme (emulsin) in- 

 creased concentration of substratum (amygdalin) increased the 

 total quantity converted, although not proportionately, the per- 

 centage conversion being diminished ; also, addition of sub- 



1 That is to say, the progress of the reaction when a definite amount of 

 enzyme had been added initially ; the effects of variation in amount of enzyme 

 acting for equal times had previously been studied by Brxicke, Schiitz, and 

 others. 



E 



