Does the Michaelis-Menten Model Fit

Perhaps the second most elementary (and very common) consideration regarding the kinetic profiling of an enzyme reaction is to assess whether or not it can be fitted to the Michaehs-Menten model. This assessment is not always taken as seriously as it should. Rather than truly assess whether or not the data conform to a Michaehs-Menten model, it is often simply stated (or bhndly assumed) that they do, and various linear transformations are conducted to arrive at estimations of the kinetic constants Km and Vmax- 

Although the data in Fig. 14.2 may appear to be visually consistent with a rectangular hyperbola pattern (Michaehs-Menten model), it is a rather simple matter to test the observed data for fit to the Michaelis-Menten 

The kinetics of the enzyme reaction are more complicated than a Michaelis-Menten model can accommodate (further diagnostic tests, such as the use of the Hill plot, may reveal allosteric behavior or cooperativity as a kinetic characteristic). 

The estimation and discussion of Km (the MichaeMs constant) may be irrelevant because Km is a constant defined by (and confined within) use of the Michaelis-Menten model (hyperbolic kinetics) in the first place. 

Different kinetic models have different conventions, and in the case of cooperative enzyme kinetic behavior, the term Ko,s is used in a sense analogous to Km for hyperbolic enzymes. In fact, transforming the original data in Fig. 14.2 to a Hill plot. 

---