Cytochrome P450 enzymes (CYPs) are a large superfamily of heme-containing monooxygenase enzymes that are found in animals, plants, and microorganisms. In humans, CYPs are primarily expressed in the liver and are involved in the metabolism of many medications and toxins. The naming of CYPs indicates the gene family, subfamily, and specific gene. Many drugs are metabolized by CYP enzymes in the liver, with CYP1A2, 2C9, 2C19, 2D6, 3A4, and 3A5 responsible for metabolizing around 90% of clinically used drugs. Variants in CYP genes can result in altered drug metabolism among individuals. Drug

1. Cytochrome P450
Enzymes
Kimberly M. Treier
PharmD Candidate 2016
4 May 2016

2. What Are They?
O Monooxygenase enzymes from the
cytochrome P450 genes
O Humans, plants, animals, prokaryotes
O Humans: ~60 CYP genes
O Arabidopsis: >250 genes
O Arose from gene duplication and
divergence
O Ranging substrate specificity

3. How Are They Named?
O Membrane-bound within a cell (cyto) +
heme pigment (chrome and P) + absorbs
light at 450 nM (450) when exposed to CO
O CYP – cytochrome P450 gene
superfamily
O Number – specific group within the gene
family
O Letter – gene’s subfamily
O Number – specific gene within the
subfamily
O E.g. CYP3A4

4. Where Are They?
O Within the body:
O Throughout
O Primarily in the liver
O Within the cell:
O Endoplasmic reticulum
O Primarily metabolize external substances
(e.g. medications and environmental
pollutants)
O Mitochondria
O Primarily metabolize internal substances

5. What Do They Do?
O Participate in synthesis and metabolism
of molecules and chemicals within cells
O Synthesis: steroid hormones, fats (e.g.
cholesterol, fatty acids) and digestive
acids (e.g. bile acids)
O Metabolism: medications, internal
substances, intracellular toxins
O Essential for normal development,
homeostasis and defense

6. How Do They Work?
O Basic reactions:
O Oxygenation, sulfoxidation, hydroxylation,
reduction, dealkylation, demethylation
epoxide formation, 1,2 migration
O Complex enzymatic reactions:
O Halide (iodine, bromine, chlorine)
oxygenation, aromatic dehalogenation, ring
expansion, ring coupling, etc.

7. Image courtesy of Google Images

8. How Do They Work?
O Most CYP P450s use a NAD(P)H-driven
redox partner system
O Donate 2 e- to reduce ferric heme
iron and ferrous-oxide species

9. Drug Metabolism
O CYP1A2, 2C9, 2C19, 2D6, 3A4 and 3A5
metabolize 90% of drugs
O Substrate metabolism:
O Activation (e.g. tramadol, losartan)
O Inactivation (e.g. simvastatin)
O Via single enzyme (e.g. metoprolol –
CYP2D6)
O Via multiple enzymes (e.g. warfarin –
CYP1A2, 2D6, 3A4)

10. Cambridge MedChem Consulting (2012). Available at:
http://www.cambridgemedchemconsulting.com/resources/ADME/metabolism.html (accessed 3 May 2016)

11. Pharmacogenetics
O CYP gene = 2 alleles
O Wild-type (wt) most common in general
population
O Variant: usually encode CYP with reduced or
no activity
O Metabolizers:
O 2 wt alleles = “extensive”
O 2 variant alleles = “poor”
O 1 wt + 1 variant = “reduced”
O Multiple wt allele copies = “ultrarapid”

12. Drug Interactions
O CYP inhibitors decrease enzymatic
activity
O Effect is immediate
O Drugs can:
O be a substrate and inhibitor of the same
enzyme (e.g. erythromycin)
O be metabolized by one enzyme and inhibit
another (e.g. terbinafiine)
O be used strategically (e.g. ritonavir added
to decrease lopinavir degradation by
CYP3A4)

13. Drug Interactions
O CYP inducers increase enzyme synthesis
O Effect is delayed
O E.g. decreased substrate concentration
within 24 hours (rifampin) or up to one
week (phenobarbital)
O Drugs can:
O be a substrate and inducer of the same
enzyme (e.g. carbamazepine)
O induce other enzymes

14. American Academy of Family Physicians, 2007

15. American Academy of Family Physicians, 2007

16. Genotype Testing
O Detect CYP450 polymorphisms
O Amplichip CYP450 test
O DNA microarray
O Detect 29 CYP2D6 polymorphisms and 2
CYP2C19 polymorphisms

17. Bacterial P450 Applications
O “The ability of P450s to perform
regioselective and often stereoselective
oxidation of their substrates makes them
attractive catalysts for applications in
synthetic biology and in the generation of
high value oxychemicals that may not be
economical to produce by synthetic
chemistry”
Girvan HM, Munro, AW. Applications of microbial cytochrome P450 enzymes in biotechnology and synthetic biology. Current Opinion
in Chemical Biology. 2016;31:136-146.

18. Bacterial P450 Models
O Protein engineering, rational
mutagenesis, etc.
O Ex: P450 BM3 (fusion protein with high
catalytic rate)
O Omeprazole – increased active site space
and conformational change  drug
oxidation mimicking human CYP2C19
O Diclofenac metabolism
O 17-beta-estradiol

19. Girvan HM, Munro, AW. Applications of microbial cytochrome P450 enzymes in biotechnology and synthetic biology. Current Opinion
in Chemical Biology. 2016;31:136-146.

20. References
Cytochrome p450. NIG U.S. National Library of Medicine. Available at:
https://ghr.nlm.nih.gov/primer/genefamily/cytochromep450 (Accessed 3 May
2016)
Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H
Freeman; 2002. Section 26.4, Important Derivatives of Cholesterol Include Bile
Salts and Steroid Hormones. Available from:
http://www.ncbi.nlm.nih.gov/books/NBK22339/
Isin EM, Guengerich FP. Complex reactions catalyzed by cytochrome P450
enzymes. Biochimica et Biophysica Acta. 2007;1770(3):314-329
Lynch T, Price A. The Effect of Cytochrome P450 Metabolism on Drug Response,
Interactions, and Adverse Effects. American Academy of Family Physicians
2007;76(3):391-396
Girvan HM, Munro, AW. Applications of microbial cytochrome P450 enzymes in
biotechnology and synthetic biology. Current Opinion in Chemical Biology.
2016;31:136-146.

21. Last presentation ever!