CATALYSIS AND ENZYMES 329 



the attention of those who wish to prevent men at any particular age from taking part in the 

 work c f the world. 



Galileo was over seventy years of age when he wrote one of his best works, and thought out, 

 amongst other things, the application of the pendulum to the regulation of clocks. In one of 

 Leeuwenhoek's letters we find the words: "A certain gentleman, who was with me some 

 months ago, intreated me to go on in making observations, adding that the fruit which 

 ripen'd in autumn was the most lasting. This is now the autumn of my life, I being arrived 

 at the age of 88J years " (H. G. Plimmer, 1913, p. 135). Many other instances might be 

 given, from the sphere of "action" as well as that of scientific discovery. 



To return to our theme. As already remarked there are various facts which 

 are calculated to give us pause before accepting, as an article of faith, the 

 doctrine of the perfect specificity of enzymes. They will be found in my 

 monograph (1913, 2, pp. 150-156) by those interested. There are one or two 

 points of general interest which may be mentioned here. 



Dakiii (1904) found that, when lipase was used for hydrolysis of the optically 

 inactive mixture of the two mandelic ethyl esters, one of the isomers was 

 hydrolysed more rapidly than the other, although finally both were completely 

 decomposed. This was brought into relation with the probable optical activity 

 of the enzymes, so that the " compounds " of this with the two forms of the ester 

 would not be symmetrical, and would therefore decompose at an unequal rate. 

 Similar facts are described by Fajans (1910) with regard to the decomposition 

 of the two camphor-carboxylic acids by optically active bases, acting as catalysts, 

 and, as regards synthesis, by Rosen thaler (1909) in the case of emulsin forming 

 benzaldehyde-cyanhydrol. We have seen that there are many cases known where 

 living organisms consume preferably the one isomer, but when this has disappeared, 

 the opposite one is also attacked. Dox and Neidig (1912) show how extracts 

 of Aspergillus hydrolyse both a- and /3-methyl glucosides, but at an unequal rate. 

 There are other cases known where extracts of tissues, which were originally 

 supposed to contain only one kind of enzyme, say maltase, have been found to 

 act, slowly, on the opposite isomer. It seems to be simpler to regard these as 

 due to a slow action of the same enzyme on both isomers than as due to 

 the presence in traces of another enzyme, especially when this other enzyme 

 is one which, under natural conditions, would never have had any opportunity 

 of action. Fajans (1910) has shown in detail how much more satisfactorily the 

 various experimental data can be explained on this hypothesis. 



The results of Erlenmeyer, mentioned above (page 285), show the possibility of an optically 

 active enzyme acting more rapidly on the appropriate component of a racemic mixture if an 

 indifferent optically active substance is present. Such a process of conversion appears to be 

 independent of chemical combination in the usual sense. 



SUMMARY 



There are a large number of reactions which proceed by themselves very 

 slowly, or sometimes, apparently, not at all, but which can be enormously 

 accelerated by the presence of small amounts of various foreign substances. 



The characteristic property of such accelerating agents, known as " catalysts," 

 is that they do not form part of the system in its final equilibrium, and either 

 appear at the end in their original form or, in some cases, are partially destroyed 

 or removed from the sphere of action in the form of constituents of some subsidiary 

 reaction. 



When the system is one that reaches a definite equilibrium under the conditions 

 of the experiment, the position of this equilibrium is unaffected by the presence or 

 the amount of the catalyst, which merely hastens the time taken for the process, 

 and this in proportion to its concentration. 



Two important things are shown by this fact, namely, that the catalyst does 

 not supply or remove energy from the system, and that it accelerates both the 

 hydrolytic and synthetic components of a reversible reaction. 



In living organisms there are a large number of substances which behave like 

 catalysts, and are known as " enzymes." 



