ROBERT A. ALBERTY 



obtained. In order to determine the initial reaction velocity 

 for use in a steady-state rate equation, it is necessary to use data 

 obtained when the reaction has proceeded only to the extent of 

 a few per cent. Greater sensitivity is thus required than in 

 ordinary kinetic studies in which the reaction is followed to 

 completion. In the transient-state method even greater sensi- 

 tivity and speed are required since the concentration of any 

 enzyme-substrate complex is so small. 



Spectrophotometric methods have been especially useful 

 because of their speed, general applicability, and high sensi- 

 tivity. Chance (4) has developed spectrophotometric methods 

 extensively and has used them to study reactions in whole cells 

 and particulate suspensions as well as in solutions. 



Future progress in the field of enzyme kinetics will be de- 

 pendent to a large extent upon the development of convenient 

 and sensitive methods for the determination of reaction rates. 

 It is to be hoped that measurements of dielectric constant, 

 magnetic susceptibility, and paramagnetic and nuclear resonance 

 absorption will be developed to the point where they can be used 

 in enzyme kinetic studies to measure small changes in con- 

 centration which occur rapidly. 



Effects of Independent Variables 



DEPENDENCE OF STEADY-STATE RATE 

 UPON SUBSTRATE CONCENTRATION 



The steady-state rate of an enzymatic reaction is generally 

 found to be directly proportional to the substrate concentration 

 at low substrate concentrations and to approach a limiting value 

 at higher substrate concentrations. This dependence of the rate 

 of the enzymatic inversion of sucrose on the sucrose concentration 

 was interpreted by Michaelis and Menten (13) in terms of the 

 mechanism 



E + S . ^' ^ ES — ^ E + P (2) 



568 



