54 BACTERIOLOGICAL CHEMISTRY 



as a carrier, increasing the active concentration of one 

 or more of the reactants, which is probably the mechanism 

 of the catalytic hardening of oils by hydrogenation in 

 presence of nickel. Most theories of enzyme action 

 involve the formation of an intermediate complex between 

 substrate and enzyme, but the type of compound formed 

 and its mode of formation are as numerous as the theories. 

 Michaelis, for instance, considers that the enzyme and 

 substrate are in homogeneous solution, and that the 

 union between them is an ionic reaction. Bayliss, on 

 the other hand, believed that the substrate is specifically 

 adsorbed on to the enzyme surface and that a chemical 

 reaction then takes place at the surface, resulting in the 

 conversion of the substrate into the end product. Fodor 

 and Abderhalden regard the adsorption as being non- 

 specific, but consider that a specific decomposition of the 

 adsorbate occurs. Willstatter suggests that the enzyme 

 has a specifically reactive group, the prosthetic group, 

 which is stabilised on a colloidal (usually protein) carrier. 

 More recently Quastel and his co-workers have developed 

 Wieland's ideas of hydrogen activation as the cause of 

 oxidation to account for the behaviour of bacterial 

 oxidation and reduction enzymes. They regard an 

 enzyme as being an active centre of high energy in a 

 cell surface caused by the interplay of the affinities of 

 neighbouring molecules. The active centre is believed 

 to exert a specific power of adsorption on the substrate 

 and to activate it by distorting its electronic system, 

 rendering the adsorbed molecule of substrate unstable 

 and capable of undergoing the chemical change character- 

 istic of the enzyme. Thus an enzyme is considered to be 

 a property of the surface, but to be specific because of 

 the groupings involved. 



For further reading : — 



W. M. Bayliss, " The Natvire of Enzyme Action." Monographs on 

 Biochemistry. Longmans, Green & Co. London, 1914. 



