92 ENZYMES 



facturing cities are not spotless nor are our processes there eco- 

 nomical. Smoke, sound, and slag-heaps are universal accompani- 

 ments of a manufacturing community. Most of the processes 

 carried on in the cell have not been reproduced in the laboratory. 

 Fischer, the finest physiological chemist of this or any century, 

 has failed to synthesise the simplest protein. Fat and carbo- 

 hydrates are interconvertible in vivo but not in vitro. True, 

 steps have been taken towards the building up of a protein. 

 Polypeptides compounds containing eighteen amino acids 

 have been the crown of Fischer's efforts, but at what a cost of 

 material, time, and energy. It has been well said that laboratory 

 processes are just a roundabout way to the sink. 



How does nature accomplish her work ? What tools does she 

 use ? How does she harness her power ? 



Nature employs catalytic methods. A catalyst is defined as a 

 substance which, while not entering into the final product of the 

 reaction, alters its rate and in some cases alters the point of 

 equilibrium. A model may make this clearer. A sheet of glass 

 may be inclined at such an angle that a body placed at its upper 

 end just slips slowly to the foot. The momentum of the sliding 

 body may be insufficient to carry it to the foot of the glass plate, 

 and motion may thus stop midway down the plane. If a small 

 quantity of oil be placed either on the glass or on the bottom of 

 the weight, it will slide rapidly to the foot of the plane. The oil 

 remains unchanged. No energy has passed from the oil to the 

 weight, and yet the rate of falling and the point of equilibrium 

 have been altered. The lubricant may be taken as representing 

 a catalyst. Some one has said that a catalyst, like a tip to a waiter, 

 accelerates a reaction that otherwise would proceed with infinite 

 slowness. It takes no part in the main reaction, is adsorbed to 

 the reacting body, and may be recovered intact at the end of the 

 reaction by destruction of the substrate. 



Catalysts are of very many kinds, and the mechanism of their 

 action is so varied and so little understood that few, if any, 

 general principles can be -enunciated. They may be classified 

 according to the means they adopt to influence a reaction. 



1. Contact agents. Many reactions seem to be accelerated by 

 the adsorption of the reacting substance on the surface of the 

 catalyst, e.g. effect of colloidal catalysts. 



Colloids, as we have seen, are characterised by the development 

 of surface. If we take a sphere of metal which just fits into a 

 cubical box, and divide that sphere into smaller spheres of uniform 



