116 LIFE: ITS NATURE AND ORIGIN 



variety of secondary but highly specific catalysts (enzymes), whose 

 production is in some way interwoven with the activities of the 

 truly living, self-reproducing catalysts. The experimental evidence 

 indicates that large numbers of biocatalyst units are destroyed or 

 inactivated in the course of their functioning, so that there must 

 be a continual replenishment of the supply. 



How do biocatalysts arise? The broadest, and therefore the 

 most indefinite answer to this question would be: by the assem- 

 blage of smaller units (atoms, molecules, colloidal particles) so as 

 to constitute an exposed surface which has a suitable electronic 

 structure and contour. Genes in the chromosome string thus form 

 duplicates of themselves (autocatalysis), and must therefore be 

 considered as living. On the other hand, an active catalyst area 

 may be formed by being built into or upon a larger fixed surface, 

 e.g., a cell wall; or else there may be formed by adsorption and/or 

 chemical combination, colloidally dispersed units — the multitu- 

 dinous enzymes — which can flow and kinetically "swim" about in 

 cytoplasm, sap, or body fluids, and may even diffuse slowly. Texts 

 often give the erroneous impression that colloids will not diffuse; 

 but Thomas Graham 33 clearly pointed out that they may diffuse, 

 though they "are slow in the extreme." 



The catalytic effect of the walls of the containers in which chem- 

 ical reactions are carried out is not, as a rule, sufficiently appreci- 

 ated, and traces of substances existing in, forming on, or intro- 

 duced into these surfaces may powerfully influence results. Thus 

 a food product processed in aluminum vessels was deleteriously 

 affected by tiny fragments of iron left in the aluminum surfaces 

 when these were scoured with steel wool. G. Bredig 34 found that 

 by fixing amino groups to cellulose, wool, or silk fibers, organic 

 catalysts were produced which split off carbon dioxide from brom- 

 camphocarbonic acid. Although inorganic catalysts may appear 

 to be simple, e.g., platinum black, those having first-hand experi- 

 ence with commercial catalysis know how potent is the influence 

 of structure, carriers, and impurities on their functioning. 



Biocatalysts are composed mainly of complex organic molecules, 

 assembled into a delicate but specific structure. When a certain 

 molecular group enters a biocatalyst to form and characterize the 

 active catalyst area, it is termed a prosthetic group. The word 

 "prosthetic" is derived from a Greek root meaning to add to, or 

 to insert. Thus prosthetic dentistry deals with the insertion of 

 missing teeth. The prosthetic group, so to say, puts "teeth" into 



