ROBERT A. ALBERTY 



as is experimentally possible. The result of a series of steady- 

 state rate measurements at a constant temperature may be 

 expressed as a function of the concentration variables by means 

 of an empirical equation referred to as the rate equation. If 

 the rate equation is simple, that is, if it involves simple powers 

 of the concentrations of the reactants, an interpretation in terms 

 of a simple mechanism may be possible. In discussing the 

 interpretation of steady-state rate equations King (9) points out 

 that the form of the rate equation for mechanisms which consist 

 of one or more independent paths gives information regarding 

 the composition of the activated complex with respect to the 

 components of the reaction mixture whose concentrations have 

 been altered. Thus experiments in dilute aqueous solutions 

 at constant pH do not yield information as to the number of 

 protons or water molecules in the activated complex. In order 

 to determine the composition of the activated complex it is 

 also necessary to know the predominant forms of the various 

 components in solution, that is, their extent of combination 

 with hydrogen ions, metal ions, etc. The characteristics of 

 rate equations arising from particular types of effects will be 

 seen in the following section. Some types of effects, such as 

 those of ionic strength, per se, or of structural alterations of the 

 protein, may not be expressible in terms of a simple rate equa- 

 tion. The kinetic method of studying interactions of enzymes 

 with protons, metal ions, organic molecules, etc, is of special 

 interest since it provides information about a limited portion 

 of the enzyme molecule. 



Mechanisms suggested by steady-state studies may be treated 

 mathematically by assuming that the rate of change in the 

 concentration of intermediate complexes is zero. This assump- 

 tion leads to a series of simultaneous equations which can be 

 solved algebraically. The coefficients of the terms in the rate 

 equation are related to the rate constants and equilibrium con- 

 stants for steps in the mechanism, but in general the individual 

 rate constants cannot be calculated from steady-state kinetic 

 data. Much of our information on enzyme kinetics is based on 



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