116 ENZYMES 



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 

 mav 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. 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 

 size, the same mass of metal may be packed into the box regardless 

 of the size of the spheres, provided they are uniform in size. Mass 

 and total effective volume are not altered, but surface is increased. 

 The surface of a sphere is 4-77/'^. If the original sphere be divided 

 into 100 small shot, then the new surface would be 100 X ^-nr-^ 

 where r-^ = radius of small shot. Now 7\ = r v^xt)0' ^° *^^^^ *^^ 



