NATURE OF THE INTERMEDIATE COMPLEXES 27 



the true or thermodynamic equilibrium constant (KJ) is related to the 

 determined or classic equilibrium constant by the expression: 



j^ , deds VeV, (E)(S) y,y, 



Ks = = ,-p.^, = A, (2-22) 



Ces Yes (-l^fe) Yes 



If free energy values are to be obtained from substrate constants, KJ should 

 be used, and when the experimentally determined Kg differs appreciably 

 from KJ these energy values may be in error. The ionic fractions of the 

 enzyme active center are generally present at activities less than their con- 

 centrations and the factor yeYslVes may deviate appreciably from unity. 



Additional Remarks Pertaining to the Validity of the Michaelis-Menten 



Treatment 



The foregoing evaluation of the assumptions of the original Michaelis- 

 Menten formulation make it apparent that although the fundamental con- 

 cept of a substrate-enzyme complex is quite well established, the data ob- 

 tained experimentally cannot usually be interpreted in a simple manner, 

 particularly with regard to the Michaelis constant Ky,^. This applies to re- 

 latively simple enzyme reactions. Many important enzyme reactions are 

 being found to be more complex than those systems upon which the theory 

 was based, and the complications of activators, coenzymes, donors and 

 acceptors, polycomplexes, and catenary reactions, make it evident that 

 the basic Michaelis-Menten equation has only a limited range of applicability. 

 Many instances might be cited where misinterpretation of the results might 

 occur using the simple theory. A particularly illuminating example is pro- 

 vided by glucose oxidase (notatin), a relatively simple enzyme system, in 

 the discussion of the conclusions of Slater by Dixon, Laidler, Ingraham, 

 and Bernard (Slater, 1955, pp. 301-312). Certain of these more complex 

 systems and the extensions that must be made to the original theory will 

 be discussed briefly in a subsequent section. 



NATURE OF THE INTERMEDIATE COMPLEXES WITH THE 



ENZYME 



A brief discussion of the molecular mechanisms of enzyme catalysis will 

 be presented in this section since it is only against such a background that 

 the many types of inhibition may be visualized and interioreted. The bind- 

 ing of the substrate to the enzyme to form the ES complex provokes no 

 unique problems, being one segment in the general field of interactions be- 

 tween various molecules and proteins; it is the subsequent reaction of the 

 ES complex that distinguishes the enzymic event. The forces that bind sub- 

 strates to enzyme active centers are those that are involved in molecular 



