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Current Drug Metabolism


ISSN (Print): 1389-2002
ISSN (Online): 1875-5453

Enzyme Kinetics of Cytochrome P450-Mediated Reactions

Author(s): C. Charles Lin, Thomas H. Rushmore, A. David Rodrigues, Thomas A. Baillie, Paul G. Pearson, Jiunn H. Lin, James A. Yergey, Bradley K. Wong, Rominder Singh, Magang Shou, Jason S. Ngui, Wei Tang, Dan Cui, Qin Mei, Cuyue Tang, Ping Lu and Yuh Lin

Volume 2, Issue 1, 2001

Page: [17 - 36] Pages: 20

DOI: 10.2174/1389200013338784

Price: $65


The most common drug-drug interactions may be understood in terms of alterations of metabolism, associated primarily with changes in the activity of cytochrome P450 (CYP) enzymes. Kinetic parameters such as K m , V max , K i and K a , which describe metabolism-based drug interactions, are usually determined by appropriate kinetic models and may be used to predict the pharmacokinetic consequences of exposure to one or multiple drugs. According to classic Michaelis-Menten (M-M) kinetics, one binding site models can be employed to simply interpret inhibition (pure competitive, non-competitive and uncompetitive) or activation of the enzyme. However, some cytochromes P450, in particular CYP3A4, exhibit unusual kinetic characteristics. In this instance, the changes in apparent kinetic constants in the presence of inhibitor or activator or second substrate do not obey the rules of M-M kinetics, and the resulting kinetics are not straightforward and hamper mechanistic interpretation of the interaction in question. These unusual kinetics include substrate activation (autoactivation), substrate inhibition, partial inhibition, activation, differential kinetics and others. To address this problem, several kinetic models can be proposed, based upon the assumption that multiple substrate binding sites exist at the active site of a particular P450, and the resulting kinetic constants are, therefore, solved to adequately describe the observed interaction between multiple drugs. The following is an overview of some cytochrome P450-mediated classic and atypical enzyme kinetics, and the associated kinetic models. Applications of these kinetic models can provide some new insights into the mechanism of P450-mediated drug-drug interactions.

Keywords: cytochrome P450 enzymes, MICHAELIS MENTEN KINETICS, Differential Kinetics, Losartan, Alpha Naphthoflavone

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