214 Dr. G. Senter. [June 2, 



temperature coefficient of the haemase catalysis for 10 is 1-5, which 

 agrees with that found by Brunner for the velocity of solution of 

 ben zoic acid in water, but is much smaller than the average for 

 reactions in a homogeneous system.* 



I have previously shown that while the reaction velocity in very 

 dilute solutions is proportional to the hydrogen-peroxide concentration, 

 in stronger solutions deviations occur, f which can be summed up by 

 saying that the reaction proceeds more rapidly in the relatively more 

 dilute peroxide solutions. On the diffusion hypothesis this can be 

 simply explained on the assumption that the diffusion process is more 

 disturbed in strong solutions by the oxygen given off from the surface 

 of the particles. 



While the above hypothesis affords a simple explanation of all the 

 facts in the hsemase catalysis, it by no means follows that it can be 

 extended to enzyme actions in general. The assumption made is that 

 the reaction at the surface is much quicker than the diffusion changes 

 concerned, and, while this is so in the dissolving of magnesia by acids, 

 and, in all probability, in the catalysis of hydrogen peroxide by hsemase 

 and by platinum, it may not be so in reactions between enzymes and 

 more complicated substances. J 



As regards the catalysis itself, it may be said with certainty that it 

 is not due to the large surface area of the colloid particles acting 

 mechanically on the peroxide, since many colloidal solutions have no 

 catalytic effect whatever. It may be due to the formation of a 

 chemical compound between the peroxide and the enzyme, which, 

 being unstable, breaks down into water, oxygen, and the enzyme, or 

 the compound may enter into double decomposition with another 

 molecule of the peroxide. Two observations which I have made may 

 contribute something to the elucidation of these changes. As mentioned 

 on p. 212 oxidations are not accelerated during the catalysis, so that 



* van't Hoff, ' Yorlesungen,' vol. 1, p. 225. 



t Senter, loc. cit., p. 286. 



Since this paper was written my attention has been drawn to a paper by 

 Herzog (' Zeit. fur physiolog. Chemie,' vol. 41, p. 416 (1904).), in which the attempt 

 is made to apply Nernst's diffusion hypothesis to all enzyme actions. Without 

 further investigation it is impossible to pronounce a definite opinion on the matter, 

 and Herzog's re-calculations of Henri's results scarcely serve to prove the truth of 

 his premises. Having regard to the results of Henri (' Lois Generates de 1' Action des 

 Diastases,' Paris, 1903), A. J. Brown (' Journ. Chem. Soc.,' vol. 81, p. 393, 1902), 

 and others, and to the temperature coefficient of enzyme actions as determined by 

 O'Sullivan and Tompson (' Journ. Chem. Soc.,' vol. 59, Part I, p. 834 (1890)), and 

 Muller-Thurgan ('Thiels Wirtschaftliche Jahrbuch,' 1885, p. 795), it seems not 

 unlikely that the relative parts played by diffusion and by the actual chemical 

 change in determining the reaction velocity depend upon the conditions of 

 experiment. 



Compare Kastle and Loevenhart, ' Am. Ch. J.,' vol. 29, pp. 397 and 

 (1903). 



