UNIT 4.19 Measurement of Human Cytochrome P4501A2 (CYP1A2) Activity In Vitro

  1. Thomas M. Polasek,
  2. David J. Elliot,
  3. John O. Miners

Published Online: 1 MAR 2006

DOI: 10.1002/0471140856.tx0419s27

Current Protocols in Toxicology

Current Protocols in Toxicology

How to Cite

Polasek, T. M., Elliot, D. J. and Miners, J. O. 2006. Measurement of Human Cytochrome P4501A2 (CYP1A2) Activity In Vitro. Current Protocols in Toxicology. 27:4.19:4.19.1–4.19.11.

Author Information

  1. Flinders Medical Centre and Flinders University School of Medicine, Bedford Park, Australia

Publication History

  1. Published Online: 1 MAR 2006
  2. Published Print: FEB 2006


Cytochrome P4501A2 (CYP1A2) is responsible for the metabolism of a diverse range of clinically used drugs and dietary and environmental chemicals (including many procarcinogens). CYP1A2 expression is influenced by numerous factors, and hence wide interindividual variability is a characteristic feature of this enzyme in humans. Phenacetin represents a convenient probe for the assessment of human CYP1A2 activity in vitro (hepatic microsomes and recombinant enzyme). It is a relatively high-turnover substrate that forms only one major primary metabolite, the O-deethylated derivative acetaminophen. Acetaminophen formation in incubations of phenacetin with a CYP1A2 source is readily measured by HPLC with UV detection. The assay has a low requirement for human liver microsomes or recombinant enzyme, and is both selective and sensitive without the requirement for a solvent extraction step. Overall assay reproducibility is excellent, with coefficients of variation <4%.


  • cytochrome P4501A2;
  • CYP1A2;
  • phenacetin O-deethylation;
  • high performance liquid chromatography