What to tasks to p450’s usually help with?
Drug and lipid metabolism
What is CYP51 important for?
- Important for cholesterol synthesis
- Metabolism of antifungal (triazole) drugs
What is the general structure of a p450?
- Prismatically Shaped
- Heme center
- NEGATIVELY CHARGED cysteine interacting with heme iron
- Distinctive 10 amino acid loop at residue 400 (involves cysteine)
T or F: p450s must undergo conformational changes in order for there active site to be exposed
True
Where can p450s be found?
- ER membrane mostly
- Inner Mitochondrial membrane
Describe the topology of p450s in the ER membrane.
Transmembrane domain (contains N-terminus) attached to a CYTOSOLIC domain which contains the heme and cysteine.
Will p450s stay fixed to the ER membrane even if their transmembrane portion is removed?
Yes
What are the 2 phases of p450 drug metabolism?
O2 is added to a lipophilic substrate in 2 phases
Phase I: non water soluble (lipophilic) drug is modified to have a hydroxyl
Phase II: a sugar or glutathione is added to make the drug more water soluble
How do p450s accomplish the cleavage of a stable O=O bond?
- They used NADPH
- They require another protein to aid in electron extraction of NADPH
Describe the steps of p450 metabolism in the ER.
- Another MEMBRANE bound protein containing FAD and FMN comes along to pass electrons sequentially (NADPH –> FAD –> FMN), then:
- 2 electrons are extracted from NADPH
- electron 1 is passed along to reduce the heme iron
- OXYGEN now binds
- electron 2 comes in and allows for oxygen cleavage
a. 1 Oxygen gets added to substrate (drug)
b. 1 Oxygen gets turned into H2O
Describe the steps of p450 metabolism in the Mitochondria.
- TWO CYTOSOLIC proteins are needed:
1. FERRODOXIN REDUCTASE [containing FAD (for 2 electron extraction, w/ one electron passing)]
2. FEREDOXIN [ Fe/S containing protein]
- 2 electrons are extracted from NADPH
- electron 1 is passed along to reduce the heme iron
- OXYGEN now binds
- electron 2 comes in and allows for oxygen cleavage
a. 1 Oxygen gets added to substrate (drug)
b. 1 Oxygen gets turned into H2O
What does it mean that p450s can be induced?
- They can be turned on to detoxify new substances encountered in the environment
- Lots of active p450 means you’re probably encountering lots of harmful things causing p450 induction
What p450 that is prone to polymorphism can be detected via a chip?
CYP2D6
What p450 is most abundant in liver?
CYP3A4
What is the result of CYP2D6 polymorphism?
- Entire gene is deleted
- You can’t metabolize codeine
What causes most drug interactions?
2 different Drugs being metabolized by the same p450s often causes interaction
Suppose you take drug A and drug B and both are metabolized by CYP2D6; however B has a lower Km. Which drug will you overdose on?
- You will overdose on drug A because it doesn’t get metabolized and just enters straight into the bloostream
Why would you not want to (or want to) drink grapefruit juice before taking oxicontin?
- Grapefruit juice blocks p450s like CYP2D6 meaning the drug is not as heavily metabolized and more gets taken up into the blood.
