Encyclopedia of Systems Biology

2013 Edition
| Editors: Werner Dubitzky, Olaf Wolkenhauer, Kwang-Hyun Cho, Hiroki Yokota

Phase I Enzymes

  • Vani BrahmachariEmail author
  • Shruti Jain
Reference work entry
DOI: https://doi.org/10.1007/978-1-4419-9863-7_865



Phase I enzymes are responsible for reactions involving oxidation, reduction, and hydrolysis. Oxidation involves the enzymatic addition of oxygen or removal of hydrogen, carried out by mixed function oxidases, often in the liver. No new groups are added to the drug metabolites, but only polar groups like oxygen and hydrogen are added or removed to help the absorption of the drug more readily by the tissue. A few examples are given below:
  • Oxidation: Alcohol dehydrogenase, ADH

  • Reduction: NADPH: quinone oxidoreductase, NQO1

  • Hydrolysis: Butyrylcholinesterase, BChE


Copyright information

© Springer Science+Business Media, LLC 2013

Authors and Affiliations

  1. 1.Dr. B. R. Ambedkar Center for Biomedical Research, University of DelhiDelhiIndia