Fundamentals of Enzyme Kinetics: Michaelis-Menten and Non-Michaelis-Type (Atypical) Enzyme Kinetics

This chapter will provide a general introduction to the kinetics of enzyme-catalyzed reactions, including a general discussion of catalysts, reaction rates, and binding constants. This section will be followed by a discussion of various types of enzyme kinetics observed in drug metabolism reactions. A large number of enzymatic reactions can be adequately described by Michaelis-Menten kinetics. The Michaelis-Menten equation represents a rectangular hyperbola, with a y-asymptote at the V_max value. However, in other cases, more complex kinetic models are required to explain the observed data. Atypical kinetic profiles are believed to arise from the simultaneous binding of multiple molecules within the active site of the enzyme (Tracy and Hummel, Drug Metab Rev 36:231-242, 2004). Several cytochromes P450 (CYPs) have large active sites that enable binding of multiple molecules (Yano et al., J Biol Chem 279:38091-38094, 2004; Wester et al., J Biol Chem 279:35630-35637, 2004). Thus, atypical kinetics are not uncommon in in vitro drug metabolism studies.

Screening for Inhibitors of Kinase Autophosphorylation

Autophosphorylation of kinases influences their conformational state and can also regulate enzymatic activity. Recently, this has become an area of interest for drug discovery. Using Alk2 as an example, we present two protocols - one based on phosphate-binding Alphascreen beads, the other on coupled luminescence measurements of ADP formation - that can be used to screen for inhibitors of autophosphorylation.