102 Perspectives in Microbiology 



schemes or individual reaction sequences; rather, I shall 

 attempt to draw the necessary inferences and at least the 

 tentative conclusions that I consider are derivable from 

 our present information about metabolic pathways. Al- 

 though these are always a matter of personal selection, I 

 hope they will be of sufficient significance to provide a 

 reasonable perspective of this area of knowledge. 



Enzymes as Surface Catalysts 



In the beginning, I shall take it for granted that the 

 chemistry of the living process occurs at the surface of large 

 protein molecules. Probably no one any longer doubts that 

 enzymes are surface catalysts, that molecules are adsorbed 

 from solution, that the nature of the surface of the enzyme 

 protein is such that particular types of molecules are pref- 

 erentially adsorbed out of the many available in the cell 

 solution, and that on the enzyme surface these molecules 

 are oriented for reaction. It is further evident that many, 

 if not all, of the reaction processes take place at the molecu- 

 lar surface and because of the orientation. I would assume 

 that this is generally accepted, if only unconsciously, 

 by almost everyone working in the field of metabo- 

 lism. 



This fact of surface catalysis is implicit in all subsequent 

 discussion. But in addition to conducting its chemistry on 

 the surface of protein molecules, the living cell exploits 

 the principle of spatial separation even further by organi- 

 zation into nucleus, mitochondria, and perhaps other cell 

 regions of differing metabolic activity. And even more, 

 the cell possesses at its interface with the environment a 

 membrane endowed with unique surface properties, which 

 have far-reaching and even quite practical consequences. 

 Weighing my words with utmost care, I am prepared to 

 defend the proposition that life does not exist except in 

 cells, and that it is to utilize to the last degree the spatial 



