THE NATURE OF ENZYME ACTIVE CENTERS 



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Flexibility of Protein Structure 



It is certain that proteins are not rigid structures despite their specific 

 configurations; what one calls the specific configuration may be the end 

 result of the adaptation of the protein to the interacting molecule. The 

 polypeptide chain and the amino acid side chains may assume those con- 



Fig. 6-1. Schematic representations of some 

 possible types of active centers. The A groups 

 are responsible for the catalytic reaction while 

 the B groups serve to bind the substrate to the 

 enzyme. B may be a single chemical group or 

 may extend over a region of the surface. In 

 each case a reaction at the X-Y bond takes place. 



figurations along or around the substrate or inhibitor that provide the 

 maximal interaction energy. In other cases the specificity towards molecules 

 with respect to distances between binding groups indicates a fairly rigid 

 structure of that portion of the enzyme. If a substance fits into a cavity 



